-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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<SEC-DOCUMENT>0000716039-05-000114.txt : 20050812
<SEC-HEADER>0000716039-05-000114.hdr.sgml : 20050812
<ACCEPTANCE-DATETIME>20050812175752
ACCESSION NUMBER:		0000716039-05-000114
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050810
FILED AS OF DATE:		20050812
DATE AS OF CHANGE:		20050812

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MCCORMICK RICHARD D
		CENTRAL INDEX KEY:			0001017985

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-08483
		FILM NUMBER:		051022974

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		8477004000

	MAIL ADDRESS:	
		STREET 1:		P O BOX 66100 WHQLD
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60666

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			UNOCAL CORP
		CENTRAL INDEX KEY:			0000716039
		STANDARD INDUSTRIAL CLASSIFICATION:	CRUDE PETROLEUM & NATURAL GAS [1311]
		IRS NUMBER:				953825062
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			0901

	BUSINESS ADDRESS:	
		STREET 1:		2141 ROSECRANS AVE
		STREET 2:		STE 4000
		CITY:			EL SEGUNDO
		STATE:			CA
		ZIP:			90245
		BUSINESS PHONE:		3107267600

	MAIL ADDRESS:	
		STREET 1:		2141 ROSECRANS AVE
		STREET 2:		STE 4000
		CITY:			EL SEGUNDO
		STATE:			CA
		ZIP:			90245
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>f4formcco.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-08-10</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000716039</issuerCik>
        <issuerName>UNOCAL CORP</issuerName>
        <issuerTradingSymbol>UCL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001017985</rptOwnerCik>
            <rptOwnerName>MCCORMICK RICHARD D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O UNOCAL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>2141 ROSECRANS AVENUE, SUITE 4000</rptOwnerStreet2>
            <rptOwnerCity>EL SEGUNDO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90245</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock / $1.00 Par Value</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2005-08-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>309.9749</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>61.9405</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11490.6531</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock / $1.00 Par Value</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2005-08-10</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>11490.6531</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to the Agreement and Plan of Merger among Unocal Corporation, Chevron Corporation and Blue Merger Sub Inc. (the &quot;Merger Agreement&quot;), each share of Unocal Corporation Common Stock issued and outstanding immediately prior to the effectiveness of the merger on August 10, 2005 (the &quot;Merger&quot;), together with the Preferred Stock Purchase Rights attached thereto, was converted into the right to receive the merger consideration specified in the Merger Agreement.</footnote>
        <footnote id="F2">Stock Units credited for voluntary deferral of director
fees under the 2004 Directors' Deferred Compensation and
Restricted Stock Unit Award Plan (the &quot;Directors' Plan&quot;).</footnote>
        <footnote id="F3">In connection with the Merger, the reporting person is entitled to receive merger consideration in both cash and/or stock of Chevron Corporation for Unocal stock owned, subject to election and proration. Based on a press release issued by Chevron on August 10, 2005 announcing preliminary results of elections for merger consideration, and valuing Chevron shares at the closing price of $62.48 on August 10, 2005, the estimated value of the merger consideration to be received by the reporting person in exchange for the 3,000 Unocal shares owned by the reporting person is between $193,063 and $202,425, depending upon the election made and the final election and proration results. In connection with the Merger, each of the 8,490.6531 Director Units owned by the reporting person under the Directors' Plan was converted into Chevron Shares at the ratio of 1.068831 Chevron shares for each Unocal Stock Unit.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Paul R. Moore, Asst Secretary, Attorney-In-Fact</signatureName>
        <signatureDate>2005-08-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----