<SUBMISSION>
<ACCESSION-NUMBER>0001181431-12-049219
<TYPE>4
<PUBLIC-DOCUMENT-COUNT>1
<PERIOD>20120906
<FILING-DATE>20120907
<DATE-OF-FILING-DATE-CHANGE>20120907
<ISSUER>
<COMPANY-DATA>
<CONFORMED-NAME>CALPINE CORP
<CIK>0000916457
<ASSIGNED-SIC>4911
<IRS-NUMBER>770212977
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</COMPANY-DATA>
<BUSINESS-ADDRESS>
<STREET1>717 TEXAS AVENUE
<STREET2>SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
<PHONE>7138302000
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>717 TEXAS AVENUE
<STREET2>SUITE 1000
<CITY>HOUSTON
<STATE>TX
<ZIP>77002
</MAIL-ADDRESS>
</ISSUER>
<REPORTING-OWNER>
<OWNER-DATA>
<CONFORMED-NAME>LSP Cal Holdings I, LLC
<CIK>0001427471
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1231
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12079
<FILM-NUMBER>121079071
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>1700 BROADWAY
<STREET2>35TH FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
<PHONE>(732) 249-6750
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1700 BROADWAY
<STREET2>35TH FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
</MAIL-ADDRESS>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>rrd355459.xml
<DESCRIPTION>4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-09-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000916457</issuerCik>
        <issuerName>CALPINE CORP</issuerName>
        <issuerTradingSymbol>CPN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001427471</rptOwnerCik>
            <rptOwnerName>LSP Cal Holdings I, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1700 BROADWAY</rptOwnerStreet1>
            <rptOwnerStreet2>35TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10019</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-09-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>17450000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.80</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25460255</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">LS Power Equity Partners, L.P. (&quot;LSPEP&quot;) is the Managing Member of LSP Cal I.  Due to its relationship with LSP Cal I, LSPEP may be deemed to have shared voting and investment power with respect to the shares beneficially owned by LSP Cal I.  As such, LSPEP may be deemed to have shared beneficial ownership of the shares of which LSP Cal I is the owner.  LSPEP, however, disclaims beneficial ownership of such shares, except to the extent of its pecuniary interest therein.</footnote>
        <footnote id="F2">LS Power Partners I (&quot;Partners I&quot;) is the general partner of each of LSPEP and LS Power Equity Partners PIE I,L.P. (&quot;PIE I&quot;).  PIE I owns 100% of LSP Cal EB I, Ltd. (&quot;LSP EB I&quot;).  LSPEP, PIE I and LSP EB I are together the members of LSP Cal I.  Due to its relationship with LSP Cal I, Partners I may be deemed to have direct or indirect pecuniary interest in the Shares owned by LSP Cal I.  Partners I, however, disclaims beneficial ownership of such Shares, except to the extent of its pecuniary interest therein.  For further details relating to the Reporting Person's ownership structure, please refer to the Schedule 13D filed with the Securities and Exchange Commission on February 11, 2008, last amended on September 7, 2012.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Darpan Kapadia, Executive Vice President</signatureName>
        <signatureDate>2012-09-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
