<?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>0001178439</rptOwnerCik>
            <rptOwnerName>GRECO ROSEMARIE B</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>45.385</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>45.385</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10862.512</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>99.21</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>99.21</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>23744.802</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 10,862.512 Restricted Share Units beneficially owned following reported transaction  (35.533 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 23,744.802 Phantom Stock Units beneficially owned following reported transaction (72.695 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 26.515 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Louisa K. Cresson, Attorney-in-fact for Rosemarie B. Greco</signatureName>
        <signatureDate>2007-12-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-12-07
0000095304
SUNOCO INC
SUN
0001178439
GRECO ROSEMARIE B
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2007-12-07
4
A
0
45.385
65.543
A
Common Stock
45.385
10862.512
D
Phantom Stock Units
2007-12-07
4
A
0
99.21
65.543
A
Common Stock
99.21
23744.802
D
Not Applicable
Conversion rate is 1 for 1.
Total of 10,862.512 Restricted Share Units beneficially owned following reported transaction  (35.533 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 23,744.802 Phantom Stock Units beneficially owned following reported transaction (72.695 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 26.515 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II).
Louisa K. Cresson, Attorney-in-fact for Rosemarie B. Greco
2007-12-10