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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-06-09</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>2006-06-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8.278</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>68.182</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>8.278</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2830.423</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>2006-06-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>23.252</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>68.182</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>23.252</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7949.968</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F4">Total of 7,949.968 Phantom Stock Units beneficially owned following reported transaction.  (14.775 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 8.477 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II.)</footnote>
        <footnote id="F2">Not Applicable</footnote>
        <footnote id="F3">Total of 2,830.423 Restricted Share Units beneficially owned following reported transaction.  (3.857 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 4.422 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II.)</footnote>
        <footnote id="F1">Conversion rate is 1 for 1.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for John W. Rowe</signatureName>
        <signatureDate>2006-06-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-06-09
0000095304
SUNOCO INC
SUN
0001067838
ROWE JOHN W
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2006-06-09
4
A
0
8.278
68.182
A
Common Stock
8.278
2830.423
D
Phantom Stock Units
2006-06-09
4
A
0
23.252
68.182
A
Common Stock
23.252
7949.968
D
Total of 7,949.968 Phantom Stock Units beneficially owned following reported transaction.  (14.775 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 8.477 Phantom Stock Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II.)
Not Applicable
Total of 2,830.423 Restricted Share Units beneficially owned following reported transaction.  (3.857 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan I and 4.422 Restricted Share Units under Sunoco, Inc.'s Directors' Deferred Compensation Plan II.)
Conversion rate is 1 for 1.
John J. DiRocco, Jr., Attorney-in-fact for John W. Rowe
2006-06-09