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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-11-01</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0000805022</issuerCik>
        <issuerName>BUCKEYE PARTNERS, L.P.</issuerName>
        <issuerTradingSymbol>BPL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001198299</rptOwnerCik>
            <rptOwnerName>BAUMANN BARBARA M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE GREENWAY PLAZA</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 600</rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77046</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Limited Partner Units</value>
            </securityTitle>
            <transactionDate>
                <value>2019-11-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8667</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>41.50</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-11-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3583</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>41.50</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Limited Partner Units</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3583</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On November 1, 2019, affiliates of IFM Global Infrastructure Fund (&quot;IFM&quot;) acquired Buckeye Partners, L.P. (&quot;BPL&quot;) pursuant to that certain Agreement and Plan of Merger, dated as of May 10, 2019, among BPL, Hercules Intermediate Holdings LLC, a Delaware limited liability company and a wholly owned subsidiary of IFM, Hercules Merger Sub LLC, a Delaware limited liability company and a wholly owned subsidiary of IFM (&quot;Merger Sub&quot;), Buckeye Pipe Line Services Company, a Pennsylvania corporation, and Buckeye GP LLC, a Delaware limited liability company (the &quot;Merger Agreement&quot;). In accordance with the Merger Agreement, BPL will merge with and into Merger Sub (the &quot;Merger&quot;) with BPL surviving the Merger as a wholly owned subsidiary of IFM. At the effective time of the Merger, each outstanding limited partnership unit representing limited partner interests in BPL was converted into the right to receive $41.50 in cash, without interest.</footnote>
        <footnote id="F2">Pursuant to the Merger Agreement, on November 1, 2019, these phantom units were cancelled in exchange for a cash payment of $41.50 per unit, without interest.  Each phantom unit is the economic equivalent of one limited partner unit of BPL.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Todd J. Russo, as attorney-in-fact for Barbara M. Baumann</signatureName>
        <signatureDate>2019-11-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
