<SUBMISSION>
<ACCESSION-NUMBER>0001181431-12-049220
<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>Vega Asset Partners LP
<CIK>0001348611
<STATE-OF-INCORPORATION>DE
<FISCAL-YEAR-END>1209
</OWNER-DATA>
<FILING-VALUES>
<FORM-TYPE>4
<ACT>34
<FILE-NUMBER>001-12079
<FILM-NUMBER>121079073
</FILING-VALUES>
<BUSINESS-ADDRESS>
<STREET1>1700 BROADWAY
<STREET2>38TH FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
<PHONE>(212) 615-3450
</BUSINESS-ADDRESS>
<MAIL-ADDRESS>
<STREET1>1700 BROADWAY
<STREET2>38TH FLOOR
<CITY>NEW YORK
<STATE>NY
<ZIP>10019
</MAIL-ADDRESS>
<FORMER-NAME>
<FORMER-CONFORMED-NAME>Luminus Asset Partners LP
<DATE-CHANGED>20060104
</FORMER-NAME>
</REPORTING-OWNER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>rrd355458.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>0001348611</rptOwnerCik>
            <rptOwnerName>Vega Asset Partners LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1700 BROADWAY, 38TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></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>300000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.80</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1902250</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Vega Energy GP, LLC (&quot;Vega Energy&quot;) is the General Partner of Vega Asset Partners.  Due to its relationship with Vega Asset Partners, Vega Energy may be deemed to have shared voting and investment power with respect to the shares beneficially owned by Vega Asset Partners.  As such, Vega Energy may be deemed to have shared beneficial ownership of the Shares of which Vega Asset Partners is the owner.  Vega Energy, 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/ Paul Segal, President</signatureName>
        <signatureDate>2012-09-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SUBMISSION>
