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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_ECCE50DA88498070E17CF4261D1B84E9_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_ECCE50DA88498070E17CF4261D1B84E9" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Cash Flows From Investing Activities</link:label>
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    <link:label id="lab_ato_InfrastructureMechanismsMember_8DE0C915029F89D16A06FD4A5A2AF9B9_label_en-US" xlink:label="lab_ato_InfrastructureMechanismsMember_8DE0C915029F89D16A06FD4A5A2AF9B9" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Infrastructure Mechanisms [Member]</link:label>
    <link:label id="lab_ato_InfrastructureMechanismsMember_8DE0C915029F89D16A06FD4A5A2AF9B9_documentation_en-US" xlink:label="lab_ato_InfrastructureMechanismsMember_8DE0C915029F89D16A06FD4A5A2AF9B9" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Costs associated with capital expenditures incurred pursuant to the risk-based program for the renewal or replacement of distribution facilities, including steel service lines, that would otherwise be charged to expense. These costs are included in allowable costs for rate making purposes and future revenue will be provided to permit recovery of such incurred costs.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_InfrastructureMechanismsMember" xlink:label="loc_ato_InfrastructureMechanismsMember_8DE0C915029F89D16A06FD4A5A2AF9B9" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DeferredFuelCostsMember_EDD500D070A1F095A85DFD4A5A2A3A0B_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredFuelCostsMember_EDD500D070A1F095A85DFD4A5A2A3A0B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Deferred Gas Costs [Member]</link:label>
    <link:label id="lab_us-gaap_DeferredFuelCostsMember_EDD500D070A1F095A85DFD4A5A2A3A0B_label_en-US" xlink:label="lab_us-gaap_DeferredFuelCostsMember_EDD500D070A1F095A85DFD4A5A2A3A0B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Deferred Fuel Costs [Member]</link:label>
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    <link:label id="lab_us-gaap_DeferredProjectCostsMember_92028A5E6F1C4CE95190FD4A5A2A3BC2_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredProjectCostsMember_92028A5E6F1C4CE95190FD4A5A2A3BC2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Deferred Project Costs [Member]</link:label>
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    <link:label id="lab_ato_RateCaseCostsMember_9E125D53882120EB6D5DFD4A5A2A8899_documentation_en-US" xlink:label="lab_ato_RateCaseCostsMember_9E125D53882120EB6D5DFD4A5A2A8899" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Costs incurred during the rate making process that would otherwise be charged to expense. These costs are included in allowable costs for rate making purposes and future revenue will be provided to permit recovery of such incurred costs.</link:label>
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    <link:label id="lab_us-gaap_OtherRegulatoryAssetsLiabilitiesMember_7818949F0D672A4757A7FD4A5A2A536F_label_en-US" xlink:label="lab_us-gaap_OtherRegulatoryAssetsLiabilitiesMember_7818949F0D672A4757A7FD4A5A2A536F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Other Regulatory Assets (Liabilities) [Member]</link:label>
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    <link:label id="lab_us-gaap_RegulatoryAssets_96A3FE1B093488AA4405FD4A5A2A0886_label_en-US" xlink:label="lab_us-gaap_RegulatoryAssets_96A3FE1B093488AA4405FD4A5A2A0886" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Regulatory Assets</link:label>
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RegulatoryAssets_96A3FE1B093488AA4405FD4A5A2A0886" xlink:to="lab_us-gaap_RegulatoryAssets_96A3FE1B093488AA4405FD4A5A2A0886" xlink:type="arc" />
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    <link:label id="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E_terseLabel_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Unsecured Senior Notes Due 2034 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E_label_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Senior Notes Due 2034 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E_documentation_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2034Member_6D8FE8FF3109CB76E41BFEF0E3FCDC3E" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured 5.95% Senior Notes, due 2034</link:label>
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    <link:label id="lab_ato_UnsecuredSeniorNotesDue2041Member_DB1EB72218FD94AFFDBBFEF0E3FC721D_label_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2041Member_DB1EB72218FD94AFFDBBFEF0E3FC721D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Senior Notes Due 2041 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredSeniorNotesDue2041Member_DB1EB72218FD94AFFDBBFEF0E3FC721D_documentation_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2041Member_DB1EB72218FD94AFFDBBFEF0E3FC721D" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured 5.50% Senior Notes, due 2041</link:label>
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    <link:label id="lab_ato_UnsecuredSeniorNotesDue2043Member_E9D98626B61146D63633FEF0E3FCD453_label_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2043Member_E9D98626B61146D63633FEF0E3FCD453" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Senior Notes Due 2043 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredSeniorNotesDue2043Member_E9D98626B61146D63633FEF0E3FCD453_documentation_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2043Member_E9D98626B61146D63633FEF0E3FCD453" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured 4.15% Senior Notes, due 2043</link:label>
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    <link:label id="lab_ato_UnsecuredSeniorNotesDue2044Member_56C0DB9EC272149C59D8FEF0E3FCBE01_label_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2044Member_56C0DB9EC272149C59D8FEF0E3FCBE01" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Senior Notes Due 2044 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredSeniorNotesDue2044Member_56C0DB9EC272149C59D8FEF0E3FCBE01_documentation_en-US" xlink:label="lab_ato_UnsecuredSeniorNotesDue2044Member_56C0DB9EC272149C59D8FEF0E3FCBE01" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured 4.125% Senior Notes, Due 2044 [Member]</link:label>
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    <link:label id="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E_terseLabel_en-US" xlink:label="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Medium Term Notes Due 2025 [Member]</link:label>
    <link:label id="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E_label_en-US" xlink:label="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Medium Term Notes Due 2025 [Member]</link:label>
    <link:label id="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E_documentation_en-US" xlink:label="lab_ato_MediumTermNotesDue2025Member_49AFDC7CA2772C61429EFEF0E3FC619E" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Series A, 1995-1, 6.67%, due 2025</link:label>
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    <link:label id="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433_terseLabel_en-US" xlink:label="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Unsecured Debentures Due 2028 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433_label_en-US" xlink:label="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Debentures Due 2028 [Member]</link:label>
    <link:label id="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433_documentation_en-US" xlink:label="lab_ato_UnsecuredDebenturesDue2028Member_56F75EC2C824C172112FFEF0E3FCA433" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured 6.75% Debentures, due 2028</link:label>
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    <link:label id="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C_terseLabel_en-US" xlink:label="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Multi-Draw Term Loan Due 2019 [Member]</link:label>
    <link:label id="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C_label_en-US" xlink:label="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Multi-Draw Term Loan [Member]</link:label>
    <link:label id="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C_documentation_en-US" xlink:label="lab_ato_MultiDrawTermLoanMember_0A3B93CD3E50C8F27230FEF0E3FC678C" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">The three year, $200 million multi-draw term loan agreement with three lenders.</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentLineItems_A3EAEA41760A94DC14B7FEF0E3FC2F9F_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentLineItems_A3EAEA41760A94DC14B7FEF0E3FC2F9F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument [Line Items]</link:label>
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    <link:label id="lab_us-gaap_DebtInstrumentCarryingAmount_3C110CDD1EBD875EACD3FEF0E3FCAB6C_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentCarryingAmount_3C110CDD1EBD875EACD3FEF0E3FCAB6C" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Long-term Debt, Gross</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_F75F193610E3F994397AFEF0E3FCA4A1" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DeferredFinanceCostsNet_BE4C7E4ABCA9568789A7FEF0E3FC8BE5_terseLabel_en-US" xlink:label="lab_us-gaap_DeferredFinanceCostsNet_BE4C7E4ABCA9568789A7FEF0E3FC8BE5" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Debt Issuance Costs, Net</link:label>
    <link:label id="lab_us-gaap_DeferredFinanceCostsNet_BE4C7E4ABCA9568789A7FEF0E3FC8BE5_label_en-US" xlink:label="lab_us-gaap_DeferredFinanceCostsNet_BE4C7E4ABCA9568789A7FEF0E3FC8BE5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Issuance Costs, Net</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DeferredFinanceCostsNet" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_BE4C7E4ABCA9568789A7FEF0E3FC8BE5" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityAbstract_D4742D0FFC9BA071AFF3FEF0E3FC25A5_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityAbstract_D4742D0FFC9BA071AFF3FEF0E3FC25A5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityAbstract" xlink:label="loc_us-gaap_LineOfCreditFacilityAbstract_D4742D0FFC9BA071AFF3FEF0E3FC25A5" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityTable_AA1CCE284EE0A7939748FEF0E3FC8B42_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityTable_AA1CCE284EE0A7939748FEF0E3FC8B42" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line Of Credit Facility [Table]</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityTable_AA1CCE284EE0A7939748FEF0E3FC8B42_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityTable_AA1CCE284EE0A7939748FEF0E3FC8B42" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility [Table]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_AA1CCE284EE0A7939748FEF0E3FC8B42" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityAxis_030B178ED44DCD508179FEF0E3FC738F_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityAxis_030B178ED44DCD508179FEF0E3FC738F" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Lender Name [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="loc_us-gaap_LineOfCreditFacilityAxis_030B178ED44DCD508179FEF0E3FC738F" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityLenderDomain_BAC97A2FAC7C857BC787FEF0E3FC1898_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLenderDomain_BAC97A2FAC7C857BC787FEF0E3FC1898" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Lender [Domain]</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityLenderDomain_BAC97A2FAC7C857BC787FEF0E3FC1898_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLenderDomain_BAC97A2FAC7C857BC787FEF0E3FC1898" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Lender [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="loc_us-gaap_LineOfCreditFacilityLenderDomain_BAC97A2FAC7C857BC787FEF0E3FC1898" xlink:type="locator" />
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    <link:label id="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B_terseLabel_en-US" xlink:label="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Five Year Unsecured Revolving Credit Agreement [Member]</link:label>
    <link:label id="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B_label_en-US" xlink:label="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Five Year Unsecured Revolving Credit Agreement [Member]</link:label>
    <link:label id="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B_documentation_en-US" xlink:label="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Regulated Operations Five Year Unsecured Revolving Credit Agreement</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_FiveYearUnsecuredRevolvingCreditAgreementMember" xlink:label="loc_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:to="lab_ato_FiveYearUnsecuredRevolvingCreditAgreementMember_394D0334095CB9EACB7EFEF0E3FCD07B" xlink:type="arc" />
    <link:label id="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0_terseLabel_en-US" xlink:label="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">$15 Million Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0_label_en-US" xlink:label="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">$15 Million Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0_documentation_en-US" xlink:label="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Nonregulated Operations $15 million Revolving Credit Note with the Bank of Texas.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_A15MillionRevolvingCreditNoteMember" xlink:label="loc_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:to="lab_ato_A15MillionRevolvingCreditNoteMember_497984B8B160AB7C0FF0FEF0E3FC63B0" xlink:type="arc" />
    <link:label id="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849_terseLabel_en-US" xlink:label="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">$25 Million Bank Loan Agreement [Member]</link:label>
    <link:label id="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849_label_en-US" xlink:label="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">$25 Million Bank Loan Agreement [Member]</link:label>
    <link:label id="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849_documentation_en-US" xlink:label="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Regulated Operations $25 million Loan Agreement with Amarillo National Bank.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_A25MillionBankLoanAgreementMember" xlink:label="loc_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:to="lab_ato_A25MillionBankLoanAgreementMember_8CD7F399A69194C69D03FEF0E3FC7849" xlink:type="arc" />
    <link:label id="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3_terseLabel_en-US" xlink:label="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">$10 Million Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3_label_en-US" xlink:label="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">$10 Million Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3_documentation_en-US" xlink:label="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Regulated Operations $10 million Revolving Credit Note with the Bank of Texas.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_A10MillionRevolvingCreditNoteMember" xlink:label="loc_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:to="lab_ato_A10MillionRevolvingCreditNoteMember_41DDD5D3863CE74738D5FEF0E3FC42D3" xlink:type="arc" />
    <link:label id="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35_terseLabel_en-US" xlink:label="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">$25 Million Uncommitted Facility [Member]</link:label>
    <link:label id="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35_label_en-US" xlink:label="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">$25 Million Uncommitted Facility [Member]</link:label>
    <link:label id="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35_documentation_en-US" xlink:label="lab_ato_A25MillionUncommittedFacilityMember_5A747C23E926E97013AEFEF0E3FC0B35" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">BNP Paribas $25 million Uncommitted Facility</link:label>
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    <link:label id="lab_us-gaap_CreditFacilityAxis_0150E6C89AE2F5F93639FEF0E3FCFD61_terseLabel_en-US" xlink:label="lab_us-gaap_CreditFacilityAxis_0150E6C89AE2F5F93639FEF0E3FCFD61" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Credit Facility [Axis]</link:label>
    <link:label id="lab_us-gaap_CreditFacilityAxis_0150E6C89AE2F5F93639FEF0E3FCFD61_label_en-US" xlink:label="lab_us-gaap_CreditFacilityAxis_0150E6C89AE2F5F93639FEF0E3FCFD61" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Credit Facility [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="loc_us-gaap_CreditFacilityAxis_0150E6C89AE2F5F93639FEF0E3FCFD61" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25_terseLabel_en-US" xlink:label="lab_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Credit Facility [Domain]</link:label>
    <link:label id="lab_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25_label_en-US" xlink:label="lab_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Credit Facility [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="loc_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25" xlink:to="lab_us-gaap_CreditFacilityDomain_4B46A5FA5781FAC6CF7AFEF0E3FC9A25" xlink:type="arc" />
    <link:label id="lab_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42_terseLabel_en-US" xlink:label="lab_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Commercial Paper [Member]</link:label>
    <link:label id="lab_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42_label_en-US" xlink:label="lab_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Commercial Paper [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommercialPaperMember" xlink:label="loc_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42" xlink:to="lab_us-gaap_CommercialPaperMember_A5EA17E451EF536211F9FEF0E3FC1C42" xlink:type="arc" />
    <link:label id="lab_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97_terseLabel_en-US" xlink:label="lab_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Uncommitted Revolving Credit Facility [Member]</link:label>
    <link:label id="lab_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97_label_en-US" xlink:label="lab_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Revolving Credit Facility [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevolvingCreditFacilityMember" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97" xlink:to="lab_us-gaap_RevolvingCreditFacilityMember_16CA59EF25DCE264E0D8FEF0E40CAA97" xlink:type="arc" />
    <link:label id="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4_terseLabel_en-US" xlink:label="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Unsecured Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4_label_en-US" xlink:label="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Revolving Credit Note [Member]</link:label>
    <link:label id="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4_documentation_en-US" xlink:label="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured revolving credit facility, used primarily to issue letters of credit.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_UnsecuredRevolvingCreditNoteMember" xlink:label="loc_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:to="lab_ato_UnsecuredRevolvingCreditNoteMember_456F4AF8B3906256057AFEF0E40C63C4" xlink:type="arc" />
    <link:label id="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA_terseLabel_en-US" xlink:label="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Unsecured Loan Agreement [Member]</link:label>
    <link:label id="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA_label_en-US" xlink:label="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Unsecured Loan Agreement [Member]</link:label>
    <link:label id="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA_documentation_en-US" xlink:label="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Unsecured Loan Agreement</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_UnsecuredLoanAgreementMember" xlink:label="loc_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:to="lab_ato_UnsecuredLoanAgreementMember_57B2E8B0F5FB79E3E552FEF0E40CD0DA" xlink:type="arc" />
    <link:label id="lab_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF_terseLabel_en-US" xlink:label="lab_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Regulation Status [Axis]</link:label>
    <link:label id="lab_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF_label_en-US" xlink:label="lab_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Regulation Status [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis" xlink:label="loc_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF" xlink:to="lab_us-gaap_PublicUtilityRegulatedOrUnregulatedStatusAxis_209452C4CD79AF229231FEF0E40CC6DF" xlink:type="arc" />
    <link:label id="lab_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660_terseLabel_en-US" xlink:label="lab_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Regulated and Unregulated Operation [Domain]</link:label>
    <link:label id="lab_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660_label_en-US" xlink:label="lab_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Regulated and Unregulated Operation [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatedAndUnregulatedOperationDomain" xlink:label="loc_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660" xlink:to="lab_us-gaap_RegulatedAndUnregulatedOperationDomain_7E9F4C9C2B19E0F0CBD3FEF0E40CE660" xlink:type="arc" />
    <link:label id="lab_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27_terseLabel_en-US" xlink:label="lab_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Regulated Operation [Member]</link:label>
    <link:label id="lab_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27_label_en-US" xlink:label="lab_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Regulated Operation [Member]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RegulatedOperationMember" xlink:label="loc_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27" xlink:to="lab_us-gaap_RegulatedOperationMember_7DBF5E527F22D00CF4D4FEF0E40C3F27" xlink:type="arc" />
    <link:label id="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239_terseLabel_en-US" xlink:label="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Covenant Compliance [Axis]</link:label>
    <link:label id="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239_label_en-US" xlink:label="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Covenant Compliance [Axis]</link:label>
    <link:label id="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239_documentation_en-US" xlink:label="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Stating compliance with debt covenants through the value required by the covenant and the actual value for the period.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_CovenantComplianceAxis" xlink:label="loc_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:to="lab_ato_CovenantComplianceAxis_38B2FE4252CA9D11E69EFEF0E40CE239" xlink:type="arc" />
    <link:label id="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7_terseLabel_en-US" xlink:label="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Covenant Compliance [Domain]</link:label>
    <link:label id="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7_label_en-US" xlink:label="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Covenant Compliance [Domain]</link:label>
    <link:label id="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7_documentation_en-US" xlink:label="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">[Domain] for Stating compliance with debt covenants through the value required by the covenant and the actual value for the period.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_CovenantComplianceDomain" xlink:label="loc_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:to="lab_ato_CovenantComplianceDomain_E902B944B5A467E90841FEF0E40C97C7" xlink:type="arc" />
    <link:label id="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390_terseLabel_en-US" xlink:label="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Required by Covenant [Member]</link:label>
    <link:label id="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390_label_en-US" xlink:label="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Required by Covenant [Member]</link:label>
    <link:label id="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390_documentation_en-US" xlink:label="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Required value stated in the debt covenant.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_RequiredbyCovenantMember" xlink:label="loc_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:to="lab_ato_RequiredbyCovenantMember_DD760F8DE2ED162941AFFEF0E40CC390" xlink:type="arc" />
    <link:label id="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3_terseLabel_en-US" xlink:label="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Actual [Member]</link:label>
    <link:label id="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3_label_en-US" xlink:label="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Actual [Member]</link:label>
    <link:label id="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3_documentation_en-US" xlink:label="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Actual value achieved, and compared to the value required within the debt covenant.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_ActualMember" xlink:label="loc_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:to="lab_ato_ActualMember_B736EDD83AF2D473E90DFEF0E40C59E3" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line Of Credit Facility [Line Items]</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20" xlink:to="lab_us-gaap_LineOfCreditFacilityLineItems_ABCB0B100C22FF3A85B6FEF0E40C5E20" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Maximum Borrowing Capacity</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Maximum Borrowing Capacity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D" xlink:to="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_81D4F44870AA5A56C5D7FEF0E40CA72D" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Remaining Borrowing Capacity</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Remaining Borrowing Capacity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF" xlink:to="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_6DA3905D8B9FD38EAEF3FEF0E40C76BF" xlink:type="arc" />
    <link:label id="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67_terseLabel_en-US" xlink:label="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Ratio of Total Debt to Total Capital</link:label>
    <link:label id="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67_label_en-US" xlink:label="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Ratio of Total Debt to Total Capital</link:label>
    <link:label id="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67_documentation_en-US" xlink:label="lab_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">For covenant purposes, total debt divided by total capitalization including original issue discount, short-term debt, capital leases, operating leases and guaranty obligations.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_RatioofTotalDebttoTotalCapital" xlink:label="loc_ato_RatioofTotalDebttoTotalCapital_377532A8FF2780475DBBFEF0E40CDD67" xlink:type="locator" />
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    <link:label id="lab_ato_ExcessofDebt_553312E9939CE9D749ACFEF0E40C6DE0_terseLabel_en-US" xlink:label="lab_ato_ExcessofDebt_553312E9939CE9D749ACFEF0E40C6DE0" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Excess of Debt</link:label>
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    <link:label id="lab_ato_ExcessofDebt_553312E9939CE9D749ACFEF0E40C6DE0_documentation_en-US" xlink:label="lab_ato_ExcessofDebt_553312E9939CE9D749ACFEF0E40C6DE0" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Total outstanding indebtedness arising out of any other credit agreements, as stated in the public debt indentures relating to senior notes and debentures, as well as certain revolving credit agreements.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_ExcessofDebt" xlink:label="loc_ato_ExcessofDebt_553312E9939CE9D749ACFEF0E40C6DE0" xlink:type="locator" />
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    <link:label id="lab_ato_LineofCreditFacilityAccordionFeature_16B7A44AB2AFE7D75F6EFEF0E40C6048_terseLabel_en-US" xlink:label="lab_ato_LineofCreditFacilityAccordionFeature_16B7A44AB2AFE7D75F6EFEF0E40C6048" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Accordion Feature</link:label>
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    <link:label id="lab_ato_LineofCreditFacilityAccordionFeature_16B7A44AB2AFE7D75F6EFEF0E40C6048_documentation_en-US" xlink:label="lab_ato_LineofCreditFacilityAccordionFeature_16B7A44AB2AFE7D75F6EFEF0E40C6048" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Monetary value of the accordion feature, the additional line of credit portion that could be borrowed against with the approval of the issuing banks.</link:label>
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    <link:label id="lab_ato_LineOfCreditFacilityMaximumBorrowingCapacityWithAccordionFeature_C806F2EC7155C9346812FEF0E40C00CF_label_en-US" xlink:label="lab_ato_LineOfCreditFacilityMaximumBorrowingCapacityWithAccordionFeature_C806F2EC7155C9346812FEF0E40C00CF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Maximum Borrowing Capacity with Accordion Feature</link:label>
    <link:label id="lab_ato_LineOfCreditFacilityMaximumBorrowingCapacityWithAccordionFeature_C806F2EC7155C9346812FEF0E40C00CF_documentation_en-US" xlink:label="lab_ato_LineOfCreditFacilityMaximumBorrowingCapacityWithAccordionFeature_C806F2EC7155C9346812FEF0E40C00CF" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Maximum available borrowing capacity under the credit facility with consideration of any additional commited line portions under the accordion feature that could be borrowed against with the approval of the issuing banks.</link:label>
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    <link:label id="lab_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_4D16B6A16D55697463D1FEF0E40CDDB6_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_4D16B6A16D55697463D1FEF0E40CDDB6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Fair Value of Amount Outstanding</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding" xlink:label="loc_us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding_4D16B6A16D55697463D1FEF0E40CDDB6" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityExpirationDate1_6C49042F6D222F939D9DFEF0E40C8CFC_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityExpirationDate1_6C49042F6D222F939D9DFEF0E40C8CFC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Expiration Date</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityExpirationDate1_6C49042F6D222F939D9DFEF0E40C8CFC_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityExpirationDate1_6C49042F6D222F939D9DFEF0E40C8CFC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Expiration Date</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="loc_us-gaap_LineOfCreditFacilityExpirationDate1_6C49042F6D222F939D9DFEF0E40C8CFC" xlink:type="locator" />
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    <link:label id="lab_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A_terseLabel_en-US" xlink:label="lab_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Equity to Capitalization Ratio</link:label>
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    <link:label id="lab_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A_documentation_en-US" xlink:label="lab_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Equity to Capitalization Ratio</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_EquitytoCapitalizationRatio" xlink:label="loc_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A" xlink:to="lab_ato_EquitytoCapitalizationRatio_B36D9EF0E1F03F162374FEF3DE48482A" xlink:type="arc" />
    <link:label id="lab_us-gaap_LongTermDebtOtherDisclosuresAbstract_CCDA41FB3B7CE017242AFEF0E40C6266_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtOtherDisclosuresAbstract_CCDA41FB3B7CE017242AFEF0E40C6266" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Long Term Debt Other Disclosures [Abstract]</link:label>
    <link:label id="lab_us-gaap_LongTermDebtOtherDisclosuresAbstract_CCDA41FB3B7CE017242AFEF0E40C6266_label_en-US" xlink:label="lab_us-gaap_LongTermDebtOtherDisclosuresAbstract_CCDA41FB3B7CE017242AFEF0E40C6266" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Long-term Debt, Other Disclosures [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtOtherDisclosuresAbstract" xlink:label="loc_us-gaap_LongTermDebtOtherDisclosuresAbstract_CCDA41FB3B7CE017242AFEF0E40C6266" xlink:type="locator" />
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    <link:label id="lab_ato_TermLoanAgreementMaximumBorrowingCapacity_14A0D23918A7A8FA642FFEF0E40CE105_label_en-US" xlink:label="lab_ato_TermLoanAgreementMaximumBorrowingCapacity_14A0D23918A7A8FA642FFEF0E40CE105" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Term Loan Agreement, Maximum Borrowing Capacity</link:label>
    <link:label id="lab_ato_TermLoanAgreementMaximumBorrowingCapacity_14A0D23918A7A8FA642FFEF0E40CE105_documentation_en-US" xlink:label="lab_ato_TermLoanAgreementMaximumBorrowingCapacity_14A0D23918A7A8FA642FFEF0E40CE105" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">The maximum borrowing capacity under a multi-draw term loan agreement.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_TermLoanAgreementMaximumBorrowingCapacity" xlink:label="loc_ato_TermLoanAgreementMaximumBorrowingCapacity_14A0D23918A7A8FA642FFEF0E40CE105" xlink:type="locator" />
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    <link:label id="lab_ato_TermLoanAgreementAmountOutstanding_3B16BF915EFE80021887FEF0E40C37D6_documentation_en-US" xlink:label="lab_ato_TermLoanAgreementAmountOutstanding_3B16BF915EFE80021887FEF0E40C37D6" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">The amount outstanding for the multi-draw term loan agreement.</link:label>
    <link:loc xlink:href="ato-20180331.xsd#ato_TermLoanAgreementAmountOutstanding" xlink:label="loc_ato_TermLoanAgreementAmountOutstanding_3B16BF915EFE80021887FEF0E40C37D6" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CommercialPaper_A98A379326AE8A6E3ED5FEF0E40C31B8_terseLabel_en-US" xlink:label="lab_us-gaap_CommercialPaper_A98A379326AE8A6E3ED5FEF0E40C31B8" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Commercial Paper</link:label>
    <link:label id="lab_us-gaap_CommercialPaper_A98A379326AE8A6E3ED5FEF0E40C31B8_label_en-US" xlink:label="lab_us-gaap_CommercialPaper_A98A379326AE8A6E3ED5FEF0E40C31B8" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Commercial Paper</link:label>
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