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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-08-29</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001393665</rptOwnerCik>
            <rptOwnerName>Elsenhans Lynn Laverty</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1735 MARKET STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PHILADELPHIA</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19103-7583</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CEO/President</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Common Stock Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2008-08-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>112663</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>112663</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>112663</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F3">Not Applicable</footnote>
        <footnote id="F1">Conversion rate is 1 for 1.</footnote>
        <footnote id="F2">Special one-time retention-based common stock units awarded in 2008 pursuant to the Sunoco, Inc. Long-Term Performance Enhancement Plan II (&quot;LTPEP II&quot;) in a transaction exempt under Rule 16b-3.  Payout of these common stock units is contingent upon continued employment with the Company through each applicable date of vesting from August 29, 2011 through August 29, 2013.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Louisa K. Cresson, Attorney-in-fact for Lynn L. Elsenhans</signatureName>
        <signatureDate>2008-09-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
[{"type": "4", "sequence": "1", "filename": "doc.xml", "description": "PRIMARY DOCUMENT", "secsgml_size_bytes": 4355}]
X0303
4
2008-08-29
0000095304
SUNOCO INC
SUN
0001393665
Elsenhans Lynn Laverty
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
1
0
0
CEO/President
Common Stock Unit
2008-08-29
4
A
0
112663
0
A
Common Stock
112663
112663
D
Not Applicable
Conversion rate is 1 for 1.
Special one-time retention-based common stock units awarded in 2008 pursuant to the Sunoco, Inc. Long-Term Performance Enhancement Plan II ("LTPEP II") in a transaction exempt under Rule 16b-3.  Payout of these common stock units is contingent upon continued employment with the Company through each applicable date of vesting from August 29, 2011 through August 29, 2013.
Louisa K. Cresson, Attorney-in-fact for Lynn L. Elsenhans
2008-09-02