<?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>0001178441</rptOwnerCik>
            <rptOwnerName>PEW ROBERT ANDERSON</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>12755.101</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>12755.101</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</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">&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.	convert, effective January 2, 2008, to Cash Units (i.e., interest-bearing cash equivalents) all account balance amounts deferred in the form of Share Units under the Sunoco, Inc. Directors' Deferred Compensation Plan I (&quot;Plan I&quot;) and the Sunoco, Inc. Directors' Deferred Compensation Plan II (&quot;Plan II&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 amounts in such converted Plan I and Plan II.&quot;</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for Robert A. Pew</signatureName>
        <signatureDate>2008-01-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2008-01-02
0000095304
SUNOCO INC
SUN
0001178441
PEW ROBERT ANDERSON
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2008-01-02
4
M
0
12755.101
70.731
D
Common Stock
12755.101
0
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.	convert, effective January 2, 2008, to Cash Units (i.e., interest-bearing cash equivalents) all account balance amounts deferred in the form of Share Units under the Sunoco, Inc. Directors' Deferred Compensation Plan I ("Plan I") and the Sunoco, Inc. Directors' Deferred Compensation Plan II ("Plan II"), 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 amounts in such converted Plan I and Plan II."
John J. DiRocco, Jr., Attorney-in-fact for Robert A. Pew
2008-01-02