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  <xs:element id="ngs_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsCancelledOrForfeitedInPeriodIntrinsicValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsCancelledOrForfeitedInPeriodIntrinsicValue" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_FederalFundRateMember" abstract="true" name="FederalFundRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_ProductSalesMember" abstract="true" name="ProductSalesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleCompressorsForExtensionOfCredit" abstract="false" name="LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleCompressorsForExtensionOfCredit" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ngs_RentalCompressorUnitWorkInProgressMember" abstract="true" name="RentalCompressorUnitWorkInProgressMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_FlaresRelatedMember" abstract="true" name="FlaresRelatedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity" abstract="false" name="LineOfCreditFacilityPotentialIncreaseInBorrowingCapacity" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityFixedChargeCoverageRatio" abstract="false" name="LineOfCreditFacilityFixedChargeCoverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ngs_IncreaseDecreaseInDeferredIncomeTaxLiabilitiesDueToChangeInTaxLaw" abstract="false" name="IncreaseDecreaseInDeferredIncomeTaxLiabilitiesDueToChangeInTaxLaw" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_RentalEquipmentGross" abstract="false" name="RentalEquipmentGross" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityLeverageRatio" abstract="false" name="LineOfCreditFacilityLeverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="ngs_InventoryNetOfReserves" abstract="false" name="InventoryNetOfReserves" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityCurrentBorrowingCapacityNetLiquidationValueOfPercentageOfEligibleCompressorsForExtensionOfCredit" abstract="false" name="LineOfCreditFacilityCurrentBorrowingCapacityNetLiquidationValueOfPercentageOfEligibleCompressorsForExtensionOfCredit" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ngs_BillAndHoldArrangementMember" abstract="true" name="BillAndHoldArrangementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount" abstract="false" name="LineOfCreditFacilityDefaultTriggerRenderingOfCertainJudgmentsAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_OperatingLeaseRightOfUseAssetAccumulatedAmortization" abstract="false" name="OperatingLeaseRightOfUseAssetAccumulatedAmortization" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_RangeFourMember" abstract="true" name="RangeFourMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_RentalContractsExcludingLargeHorsepowerCompressorsMember" abstract="true" name="RentalContractsExcludingLargeHorsepowerCompressorsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount" abstract="false" name="LineOfCreditFacilityDefaultTriggerCertainDefaultsOfOtherCompanyIndebtednessAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_InventoryValuationReservesRollForward" abstract="true" name="InventoryValuationReservesRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ngs_WeightedAverageSharesOutstandingBasicAndDilutedAbstract" abstract="true" name="WeightedAverageSharesOutstandingBasicAndDilutedAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityPotentialMaximumBorrowingCapacity" abstract="false" name="LineOfCreditFacilityPotentialMaximumBorrowingCapacity" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_OtherPartsRebuildsMember" abstract="true" name="OtherPartsRebuildsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_CompressorRelatedMember" abstract="true" name="CompressorRelatedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_InventoryAllowanceAccrual" abstract="false" name="InventoryAllowanceAccrual" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_RangeFiveMember" abstract="true" name="RangeFiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_RangeOneMember" abstract="true" name="RangeOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_NumberOfIndependentDirectors" abstract="false" name="NumberOfIndependentDirectors" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ngs_InventoryWriteOffs" abstract="false" name="InventoryWriteOffs" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentOfEligibleAccountsReceivableOwingByNonInvestmentGradeDebtors" abstract="false" name="LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentOfEligibleAccountsReceivableOwingByNonInvestmentGradeDebtors" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ngs_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" abstract="true" name="ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ngs_EurodollarRateMember" abstract="true" name="EurodollarRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ngs_LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleAccountsReceivableOwingByInvestmentGradeDebtors" abstract="false" name="LineOfCreditFacilityCurrentBorrowingCapacityComponentPercentageOfEligibleAccountsReceivableOwingByInvestmentGradeDebtors" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ngs_IntangibleAssetsAccumulatedAmortization" abstract="false" name="IntangibleAssetsAccumulatedAmortization" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>
