<?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>0001178439</rptOwnerCik>
            <rptOwnerName>GRECO ROSEMARIE B</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>24.427</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>24.427</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>608.567</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>51.547</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>51.547</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1225.781</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The conversion rate is 1 for 1.</footnote>
        <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="F3">Total of 8,797.911 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 18,565.809 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 derivate securities was effectively halved.</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>
    </footnotes>

    <ownerSignature>
        <signatureName>John J. DiRocco, Jr., Attorney-in-fact for Rosemarie B. Greco</signatureName>
        <signatureDate>2005-09-13</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-09-09
0000095304
SUNOCO INC
SUN
0001178439
GRECO ROSEMARIE B
1735 MARKET STREET
PHILADELPHIA
PA
19103-7583
1
0
0
0
Deferred Share Units
2005-09-09
4
A
0
24.427
71.835
A
1988-08-08
1988-08-08
Common Stock
24.427
608.567
D
Phantom Stock Units
2005-09-09
4
A
0
51.547
71.835
A
1988-08-08
1988-08-08
Common Stock
51.547
1225.781
D
The conversion rate is 1 for 1.
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).
Total of 8,797.911 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 18,565.809 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 derivate securities was effectively halved.
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).
John J. DiRocco, Jr., Attorney-in-fact for Rosemarie B. Greco
2005-09-13