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    <periodOfReport>2018-09-20</periodOfReport>

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    <issuer>
        <issuerCik>0001358831</issuerCik>
        <issuerName>LEGACY RESERVES LP</issuerName>
        <issuerTradingSymbol>LGCY</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001544888</rptOwnerCik>
            <rptOwnerName>Foster Micah C.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>303 W. WALL STREET, SUITE 1800</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MIDLAND</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>79701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
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            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CAO and Controller</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

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    <derivativeTable>
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            <securityTitle>
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                <value>2018-09-20</value>
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            <transactionTimeliness>
                <value></value>
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            <transactionAmounts>
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                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
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                <transactionAcquiredDisposedCode>
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                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Units</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>54605</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                    <footnoteId id="F2"/>
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                    <value>D</value>
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                <footnoteId id="F6"/>
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                    <value>Units</value>
                </underlyingSecurityTitle>
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                    <value>0</value>
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    <footnotes>
        <footnote id="F1">In connection with the corporate reorganization of the Issuer from a master limited partnership to a corporation (the &quot;Corporate Reorganization&quot;), each outstanding unit representing a limited partner interest in the Issuer (&quot;Unit&quot;) was converted into the right to receive one share of common stock, $0.01 par value per share, of Legacy Reserves Inc. (&quot;New Legacy Common Stock&quot;).</footnote>
        <footnote id="F2">Each phantom unit represents the economic equivalent of a Unit.</footnote>
        <footnote id="F3">These phantom unites were granted pursuant to an awards agreement that provided for settlement in Units and were scheduled to vest as follows: (i) 14,674 phantom units subject to vesting on February 18, 2019; (ii) 14,868 phantom units subject to vesting on February 18, 2020; and (iii) 25,063 phantom units subject to vesting on February 18, 2021.  In connection with the Corporate Reorganization, these phantom units automatically vested in full and were settled in Units.</footnote>
        <footnote id="F4">These phantom units were granted pursuant to an award agreement that provided for settlement in cash and provided for cliff vesting in the third year after grant, subject to the achievement of certain performance-based criteria during the three fiscal years prior to the vesting date.  The vesting schedule was as follows: 83,850 phantom units on February 18, 2019; (ii) 59,472 phantom units on February 19, 2010; and (iii) 150,376 phantom units on February 18, 2021.</footnote>
        <footnote id="F5">In connection with the Corporate Reorganization, 146,849 of these phantom units automatically vested in full and were settled in cash.  Another 146,849 phantom unites were forfeited.</footnote>
        <footnote id="F6">These phantom units were granted pursuant to an award agreement that provided for settlement in cash and were scheduled to vest as follows: (i) 48,214 phantom units on February 18, 2019; (ii) 29,736 phantom units on February 18, 2020; and (iii) 12,531 phantom units on February 18, 2021.  In connection with the Corporate Reorganization, these phantom units automatically vested in full and were settled in cash.</footnote>
    </footnotes>

    <remarks>Chief Accounting Officer and Controller of Legacy Reserves GP, LLC, the general partner of Legacy Reserves LP.</remarks>

    <ownerSignature>
        <signatureName>/s/ Dan G. LeRoy, as attorney-in-fact for Micah C. Foster</signatureName>
        <signatureDate>2018-09-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
