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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-12-07</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001067838</rptOwnerCik>
            <rptOwnerName>ROWE JOHN W</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>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred Share Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-12-07</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>15.491</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>65.543</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>15.491</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3707.532</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-12-07</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>45.687</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>65.543</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>45.687</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10934.627</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F2">Not Applicable</footnote>
        <footnote id="F1">Conversion rate is 1 for 1.</footnote>
        <footnote id="F3">Total of 3,707.532 Restricted Share Units beneficially owned following reported transaction  (5.639 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 9.852 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).</footnote>
        <footnote id="F4">Total of 10,934.627 Phantom Stock Units beneficially owned following reported transaction (21.602 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 24.085 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Louisa K. Cresson, Attorney-in-fact for John W. Rowe</signatureName>
        <signatureDate>2007-12-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-12-07
0000095304
SUNOCO INC
SUN
0001067838
ROWE JOHN W
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2007-12-07
4
A
0
15.491
65.543
A
Common Stock
15.491
3707.532
D
Phantom Stock Units
2007-12-07
4
A
0
45.687
65.543
A
Common Stock
45.687
10934.627
D
Not Applicable
Conversion rate is 1 for 1.
Total of 3,707.532 Restricted Share Units beneficially owned following reported transaction  (5.639 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 9.852 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).
Total of 10,934.627 Phantom Stock Units beneficially owned following reported transaction (21.602 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 24.085 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).
Louisa K. Cresson, Attorney-in-fact for John W. Rowe
2007-12-10