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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-05-04</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001178437</rptOwnerCik>
            <rptOwnerName>FAIRBAIRN URSULA F</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>2006-05-04</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>720.245</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>83.305</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>720.245</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6067.878</value>
                    <footnoteId id="F3"/>
                </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">Yearly election credit credited as Restricted Share Units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan II, in transaction exempt under Rule 16b-3(d).</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for Ursula O. Fairbairn</signatureName>
        <signatureDate>2006-05-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-05-04
0000095304
SUNOCO INC
SUN
0001178437
FAIRBAIRN URSULA F
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2006-05-04
4
A
0
720.245
83.305
A
Common Stock
720.245
6067.878
D
Not Applicable
Conversion rate is 1 for 1.
Yearly election credit credited as Restricted Share Units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan II, in transaction exempt under Rule 16b-3(d).
John J. DiRocco, Jr., Attorney-in-fact for Ursula O. Fairbairn
2006-05-08