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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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<SEC-DOCUMENT>0001140361-09-002807.txt : 20090205
<SEC-HEADER>0001140361-09-002807.hdr.sgml : 20090205
<ACCEPTANCE-DATETIME>20090205114138
ACCESSION NUMBER:		0001140361-09-002807
CONFORMED SUBMISSION TYPE:	3/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080811
FILED AS OF DATE:		20090205
DATE AS OF CHANGE:		20090205

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MILLER W. THADDEUS
		CENTRAL INDEX KEY:			0001442784

	FILING VALUES:
		FORM TYPE:		3/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-12079
		FILM NUMBER:		09570629

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		713-830-2000

	MAIL ADDRESS:	
		STREET 1:		717 TEXAS AVENUE, SUITE 1000
		CITY:			HOUSTON
		STATE:			TX
		ZIP:			77002

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CALPINE CORP
		CENTRAL INDEX KEY:			0000916457
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRIC SERVICES [4911]
		IRS NUMBER:				770212977
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		50 WEST SAN FERNANDO ST
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95113
		BUSINESS PHONE:		4089955115

	MAIL ADDRESS:	
		STREET 1:		50 W SAN FERNANDO
		STREET 2:		SUITE 500
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95113
</SEC-HEADER>
<DOCUMENT>
<TYPE>3/A
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3/A
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2008-08-11</periodOfReport>

    <dateOfOriginalSubmission>2008-08-13</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001442784</rptOwnerCik>
            <rptOwnerName>MILLER W. THADDEUS</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CALPINE CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>717 TEXAS AVENUE, SUITE 1000</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77002</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP &amp; CHIEF LEGAL OFFICER</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1083</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This amendment on Form 3 is being filed solely to add this line of ownership information. The common stock reported represents shares issued pursuant to the Issuer's Plan of Reorganization in respect of a claim related to $22,000 principal amount of the Issuer's 4.75% Contingent Convertible Senior Notes due 2023. In accordance with the Issuer's Plan of Reorganization, such convertible notes were terminated on January 31, 2008.  It is possible that additional shares of common stock may be payable in respect of claims relating to such convertible notes pursuant to the Plan of Reorganization. These shares were also omitted from the Forms 4 and 4/A filed by the reporting person after his original Form 3 was filed through the date of this Form 3/A.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>W. Thaddeus Miller</signatureName>
        <signatureDate>2009-02-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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