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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-05-25</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101778</issuerCik>
        <issuerName>MARATHON OIL CORP</issuerName>
        <issuerTradingSymbol>MRO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238369</rptOwnerCik>
            <rptOwnerName>BEHRMAN PHILIP G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MARATHON OIL CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>5555 SAN FELIPE ROAD</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77056</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. Vice Pres., WW Exploration</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-05-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>714.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37287.821</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <transactionDate>
                <value>2005-05-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2900.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>40187.821</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>COMMON STOCK</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>200.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Family Living Trust</value>
                    <footnoteId id="F3"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>47.65</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-05-25</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F4"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22700.000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2006-05-25</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-05-25</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>COMMON STOCK</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>22700.000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>22700.000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Forfeiture of restricted stock granted under Marathon Oil Corporation 1990 Stock Plan.</footnote>
        <footnote id="F2">Restricted stock granted under Marathon Oil Corporation 2003 Incentive Compensation Plan, which vests on 05/25/2008.</footnote>
        <footnote id="F3">These shares are held in The Jacqueline L. Delany Trust, pursuant to a Trust Agreement dated May 30, 2003 between Jacqueline L. Delany, as Trustor and Joan Marie Delany, as trustee.  The reporting person's mother-in-law is the beneficiary of the trust. The reporting person's spouse is the trustee of the trust and holds a remainder interest therein. The reporting person disclaims beneficial ownership of the reported securities except to the extent of his and/or his spouse's pecuniary interest therein.</footnote>
        <footnote id="F4">Grant under the Marathon Oil Corporation 2003 Incentive Compensation Plan.</footnote>
        <footnote id="F5">Vests in three cumulative annual installments of 7,566, 7,567, and 7,567 shares on May 25, 2006, 2007, and 2008, respectively.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Richard J. Kolencik, Attorney-in-Fact for Philip G. Behrman</signatureName>
        <signatureDate>2005-05-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-05-25
0
0000101778
MARATHON OIL CORP
MRO
0001238369
BEHRMAN PHILIP G
C/O MARATHON OIL CORPORATION
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
Sr. Vice Pres., WW Exploration
COMMON STOCK
2005-05-25
4
D
0
714.000
0
D
37287.821
D
COMMON STOCK
2005-05-25
4
A
0
2900.000
0
A
40187.821
D
COMMON STOCK
200.000
I
By Family Living Trust
Employee Stock Option (Right to Buy)
47.65
2005-05-25
4
A
0
22700.000
0
A
2006-05-25
2015-05-25
COMMON STOCK
22700.000
22700.000
D
Forfeiture of restricted stock granted under Marathon Oil Corporation 1990 Stock Plan.
Restricted stock granted under Marathon Oil Corporation 2003 Incentive Compensation Plan, which vests on 05/25/2008.
These shares are held in The Jacqueline L. Delany Trust, pursuant to a Trust Agreement dated May 30, 2003 between Jacqueline L. Delany, as Trustor and Joan Marie Delany, as trustee.  The reporting person's mother-in-law is the beneficiary of the trust. The reporting person's spouse is the trustee of the trust and holds a remainder interest therein. The reporting person disclaims beneficial ownership of the reported securities except to the extent of his and/or his spouse's pecuniary interest therein.
Grant under the Marathon Oil Corporation 2003 Incentive Compensation Plan.
Vests in three cumulative annual installments of 7,566, 7,567, and 7,567 shares on May 25, 2006, 2007, and 2008, respectively.
Richard J. Kolencik, Attorney-in-Fact for Philip G. Behrman
2005-05-27