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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-01-02</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001178442</rptOwnerCik>
            <rptOwnerName>RATCLIFFE GEORGE J</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>2008-01-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8504.5</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>70.731</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>8504.5</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2358.012</value>
                    <footnoteId id="F4"/>
                </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>2008-01-02</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>14655.269</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>70.731</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>14655.269</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4487.83</value>
                    <footnoteId id="F5"/>
                </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">&quot;As a Sunoco, Inc. director who will attain age 72 on or before December 2010, and in accordance with applicable Internal Revenue Service transition rules under Internal Revenue Code ?409A, the reporting person elected, on or before December 14, 2007, to do the following:
1.	effective January 2, 2008, convert to Cash Units (i.e., interest-bearing cash equivalents) the account balance amount deferred in the form of Share Units under the Sunoco, Inc. Directors' Deferred Compensation Plan I (&quot;Plan I&quot;), with each Share Unit so converted being valued at the average closing price of a share of Sunoco, Inc. common stock for the period of ten (10) trading days immediately prior to January 1, 2008; and
2.	receive, on June 25, 2008, a one-time cash payment of the Cash Unit account balance amount in such converted Plan I.&quot;</footnote>
        <footnote id="F4">Total of 2,358.012 Restricted Share Units beneficially owned under Sunoco, Inc.'s Directors' Deferred Compensation Plan II following reported transaction.</footnote>
        <footnote id="F5">Total of 4,487.83 Phantom Stock Units beneficially owned under Sunoco, Inc.'s Directors' Deferred Compensation Plan II following reported transaction.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for George J. Ratcliffe</signatureName>
        <signatureDate>2008-01-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2008-01-02
0000095304
SUNOCO INC
SUN
0001178442
RATCLIFFE GEORGE J
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2008-01-02
4
M
0
8504.5
70.731
D
Common Stock
8504.5
2358.012
D
Phantom Stock Units
2008-01-02
4
M
0
14655.269
70.731
D
Common Stock
14655.269
4487.83
D
Not Applicable
Conversion rate is 1 for 1.
"As a Sunoco, Inc. director who will attain age 72 on or before December 2010, and in accordance with applicable Internal Revenue Service transition rules under Internal Revenue Code ?409A, the reporting person elected, on or before December 14, 2007, to do the following:
1.	effective January 2, 2008, convert to Cash Units (i.e., interest-bearing cash equivalents) the account balance amount deferred in the form of Share Units under the Sunoco, Inc. Directors' Deferred Compensation Plan I ("Plan I"), with each Share Unit so converted being valued at the average closing price of a share of Sunoco, Inc. common stock for the period of ten (10) trading days immediately prior to January 1, 2008; and
2.	receive, on June 25, 2008, a one-time cash payment of the Cash Unit account balance amount in such converted Plan I."
Total of 2,358.012 Restricted Share Units beneficially owned under Sunoco, Inc.'s Directors' Deferred Compensation Plan II following reported transaction.
Total of 4,487.83 Phantom Stock Units beneficially owned under Sunoco, Inc.'s Directors' Deferred Compensation Plan II following reported transaction.
John J. DiRocco, Jr., Attorney-in-fact for George J. Ratcliffe
2008-01-02