<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
    <periodOfReport>2003-09-11</periodOfReport>
    <notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000101778</issuerCik>
        <issuerName>MARATHON OIL CORP</issuerName>
        <issuerTradingSymbol>MRO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001238370</rptOwnerCik>
            <rptOwnerName>GOLDER G DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>MARATHON OIL CORP</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. V. P.-Commercial. and Dev.</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>
  <nonDerivativeTable>
   <nonDerivativeTransaction>
      <securityTitle>
          <value>COMMON STOCK</value>
      </securityTitle>
      <transactionDate>
          <value>2003-09-11</value>
      </transactionDate>
      <transactionCoding>
          <transactionFormType>4</transactionFormType>
          <transactionCode>I</transactionCode>
          <equitySwapInvolved>0</equitySwapInvolved>
              <footnoteId id="F1" />
      </transactionCoding>
      <transactionTimeliness>
      <value />
      </transactionTimeliness>
      <transactionAmounts>
          <transactionShares>
              <value>30.931</value>
              <footnoteId id="F2" />
          </transactionShares>
          <transactionPricePerShare>
              <value>28.40</value>
          </transactionPricePerShare>
          <transactionAcquiredDisposedCode>
              <value>D</value>
          </transactionAcquiredDisposedCode>
      </transactionAmounts>
      <postTransactionAmounts>
          <sharesOwnedFollowingTransaction>
              <value>27332.000</value>
          </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
          <directOrIndirectOwnership>
              <value>D</value>
          </directOrIndirectOwnership>
      </ownershipNature>
   </nonDerivativeTransaction>
  </nonDerivativeTable>
  <derivativeTable>
   <derivativeTransaction>
      <securityTitle>
          <value>Phantom Stock</value>
      </securityTitle>
      <conversionOrExercisePrice>
              <footnoteId id="F3" />
      </conversionOrExercisePrice>
      <transactionDate>
          <value>2003-09-11</value>
      </transactionDate>
      <transactionCoding>
          <transactionFormType>4</transactionFormType>
          <transactionCode>I</transactionCode>
          <equitySwapInvolved>0</equitySwapInvolved>
              <footnoteId id="F4" />
      </transactionCoding>
      <transactionAmounts>
          <transactionShares>
              <value>10.136</value>
              <footnoteId id="F5" />
          </transactionShares>
          <transactionPricePerShare>
              <value>28.44</value>
          </transactionPricePerShare>
          <transactionAcquiredDisposedCode>
              <value>D</value>
          </transactionAcquiredDisposedCode>
      </transactionAmounts>
      <exerciseDate>
              <footnoteId id="F6" />
      </exerciseDate>
      <expirationDate>
              <footnoteId id="F7" />
      </expirationDate>
      <underlyingSecurity>
          <underlyingSecurityTitle>
              <value>COMMON STOCK</value>
          </underlyingSecurityTitle>
          <underlyingSecurityShares>
              <value>10.136</value>
          </underlyingSecurityShares>
      </underlyingSecurity>
      <postTransactionAmounts>
          <sharesOwnedFollowingTransaction>
              <value>0.000</value>
          </sharesOwnedFollowingTransaction>
      </postTransactionAmounts>
      <ownershipNature>
          <directOrIndirectOwnership>
              <value>D</value>
          </directOrIndirectOwnership>
      </ownershipNature>
   </derivativeTransaction>
  </derivativeTable>
<footnotes>
   <footnote id="F1">Transfer out of issuer stock fund into another fund in Marathon Oil CompanyThrift Plan.</footnote>
   <footnote id="F2">Includes 30.931 shares, previously not reported, for dividends allocated to issuer stock fund for reporting person's account in M
arathon Oil Company Thrift Plan. </footnote>
   <footnote id="F3">1-for-1</footnote>
   <footnote id="F4">Transfer out of issuer phantom stock fund into another fund in Marthon Oil Company Deferred Compensation Plan. </footnote>
   <footnote id="F5">Includes dividends of 10.136 shares at price of 28.64 per share, previously not reported pursuant to Rule 16a-11, for reporting p
erson's phantom stock account in the Marathon Oil Company Deferred Compensation Plan.</footnote>
   <footnote id="F6">Immediately</footnote>
   <footnote id="F7">Shares of Phantom Stock are payable in cash following the termination of the reporting person's employment.</footnote>
</footnotes>
    <ownerSignature>
       <signatureName>By: R. J. Kolencik, Attorney-in-Fact for G. David Golder</signatureName>
       <signatureDate>2003-09-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0201
4
2003-09-11
0
0000101778
MARATHON OIL CORP
MRO
0001238370
GOLDER G DAVID
MARATHON OIL CORP
5555 SAN FELIPE ROAD
HOUSTON
TX
77056
0
1
0
0
Sr. V. P.-Commercial. and Dev.
COMMON STOCK
2003-09-11
4
I
0
30.931
28.40
D
27332.000
D
Phantom Stock
2003-09-11
4
I
0
10.136
28.44
D
COMMON STOCK
10.136
0.000
D
Transfer out of issuer stock fund into another fund in Marathon Oil CompanyThrift Plan.
Includes 30.931 shares, previously not reported, for dividends allocated to issuer stock fund for reporting person's account in M
arathon Oil Company Thrift Plan.
1-for-1
Transfer out of issuer phantom stock fund into another fund in Marthon Oil Company Deferred Compensation Plan.
Includes dividends of 10.136 shares at price of 28.64 per share, previously not reported pursuant to Rule 16a-11, for reporting p
erson's phantom stock account in the Marathon Oil Company Deferred Compensation Plan.
Immediately
Shares of Phantom Stock are payable in cash following the termination of the reporting person's employment.
By: R. J. Kolencik, Attorney-in-Fact for G. David Golder
2003-09-12