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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-09-09</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>2005-09-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>14.137</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>71.835</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1988-08-08</value>
            </exerciseDate>
            <expirationDate>
                <value>1988-08-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>14.137</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>584.247</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>2005-09-09</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>29.947</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>71.835</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>1988-08-08</value>
            </exerciseDate>
            <expirationDate>
                <value>1988-08-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>29.947</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>330.159</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F2">Dividend equivalents credited as restricted share units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan, in transaction exempt under Rule 16b-3(d).</footnote>
        <footnote id="F4">Crediting of share units representing voluntary deferred compensation pursuant to the Sunoco, Inc. Directors Deferred Compensation Plan, in transactions exempt under Rule 16b-3(d).</footnote>
        <footnote id="F3">Total of 5,091.847 Restricted Share Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.</footnote>
        <footnote id="F5">Total of 10,786.329 Phantom Stock Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.</footnote>
        <footnote id="F1">The conversion rate is 1 for 1.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for Ursula F. Fairbairn</signatureName>
        <signatureDate>2005-09-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-09-09
0000095304
SUNOCO INC
SUN
0001178437
FAIRBAIRN URSULA F
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2005-09-09
4
A
0
14.137
71.835
A
1988-08-08
1988-08-08
Common Stock
14.137
584.247
D
Phantom Stock Units
2005-09-09
4
A
0
29.947
71.835
A
1988-08-08
1988-08-08
Common Stock
29.947
330.159
D
Dividend equivalents credited as restricted share units acquired pursuant to the Sunoco, Inc. Directors' Deferred Compensation Plan, in transaction exempt under Rule 16b-3(d).
Crediting of share units representing voluntary deferred compensation pursuant to the Sunoco, Inc. Directors Deferred Compensation Plan, in transactions exempt under Rule 16b-3(d).
Total of 5,091.847 Restricted Share Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.
Total of 10,786.329 Phantom Stock Units beneficially owned following reported transaction.  Reported item reflects the 2-for-1 split of Sunoco, Inc.'s Common Stock effectuated on August 1, 2005.  This stock split resulted in a doubling of the shares of Sunoco Common Stock, and related derivative securities, previously reported as being beneficially owned by the reporting person.  Also, as a result of the split, the trading price of Sunoco Common Stock and the exercise or conversion price of related derivative securities was effectively halved.
The conversion rate is 1 for 1.
John J. DiRocco, Jr., Attorney-in-fact for Ursula F. Fairbairn
2005-09-13