<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-12-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000095304</issuerCik>
        <issuerName>SUNOCO INC</issuerName>
        <issuerTradingSymbol>SUN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001174604</rptOwnerCik>
            <rptOwnerName>OWENS ROBERT W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1801 MARKET STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PHILADELPHIA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19103-1699</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Senior Vice President</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>82.56</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2004-12-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>28200</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-12-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2014-12-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>28200</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28200</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Stock options (rights to buy Sunoco, Inc. common stock) exercisable two years from the date of grant, pursuant to the Sunoco, Inc. Long Term Performance Enhancement Plan II (&quot;LTPEP II&quot;), in a transaction exempt under Rule 16b-3.  These stock options were granted with tandem appreciation rights (&quot;Limited Rights&quot;) that may be exercised for cash only in the event of a change in control of Sunoco, Inc.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ John J. DiRocco, Jr., Attorney-in-fact for</signatureName>
        <signatureDate>2004-12-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "c0001174604d20041203f4f.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 4230}]
X0202
4
2004-12-01
0
0000095304
SUNOCO INC
SUN
0001174604
OWENS ROBERT W
1801 MARKET STREET
PHILADELPHIA
PA
19103-1699
0
1
0
0
Senior Vice President
Stock Options (Right to buy)
82.56
2004-12-01
4
A
0
28200
0
A
2006-12-01
2014-12-01
Common Stock
28200
28200
D
Stock options (rights to buy Sunoco, Inc. common stock) exercisable two years from the date of grant, pursuant to the Sunoco, Inc. Long Term Performance Enhancement Plan II ("LTPEP II"), in a transaction exempt under Rule 16b-3.  These stock options were granted with tandem appreciation rights ("Limited Rights") that may be exercised for cash only in the event of a change in control of Sunoco, Inc.
/s/ John J. DiRocco, Jr., Attorney-in-fact for
2004-12-03