<?xml version="1.0"?>
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    <periodOfReport>2010-05-26</periodOfReport>

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    <issuer>
        <issuerCik>0001338613</issuerCik>
        <issuerName>Regency Energy Partners LP</issuerName>
        <issuerTradingSymbol>RGNC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001464952</rptOwnerCik>
            <rptOwnerName>Dixon Dennie W.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2001 BRYAN STREET</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 3700</rptOwnerStreet2>
            <rptOwnerCity>DALLAS</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75201</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Sr. VP Operations</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>Common Units</value>
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            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>20584</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
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                <sharesOwnedFollowingTransaction>
                    <value>25118</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>5446</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
                    <value>19672</value>
                </sharesOwnedFollowingTransaction>
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                    <value>D</value>
                </directOrIndirectOwnership>
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                <value>Phantom Units</value>
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                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionShares>
                    <value>9334</value>
                </transactionShares>
                <transactionPricePerShare>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <value>2010-05-26</value>
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            <expirationDate>
                <value>2010-05-26</value>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Units</value>
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                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9334</value>
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                    <value>2800</value>
                </sharesOwnedFollowingTransaction>
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                    <value>D</value>
                </directOrIndirectOwnership>
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        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Units</value>
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                <transactionShares>
                    <value>11250</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
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                    <value>D</value>
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            <expirationDate>
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            </expirationDate>
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                    <value>11250</value>
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    <footnotes>
        <footnote id="F1">The holder settled 100 percent of his phantom units for RGNC common units on the date of vesting.</footnote>
        <footnote id="F2">These Phantom Units were granted on May 27, 2009. 4,800 of the phantom units contractually convert into a variable number of common units based on total unitholder return over a three year period or upon a change in control. This transaction represents the vesting of the original grant of 4,800 market condition phantom units multiplied by a factor of 1.5 due to a change in control event on May 26, 2010 in accordance with the terms of the grant plus the remaining 2,134 service condition phantom units.</footnote>
        <footnote id="F3">Each Phantom Unit and Restricted Unit is the economic equivalent of one common unit representing a limited partner interest in Regency Energy Partners LP.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Dennie W. Dixon</signatureName>
        <signatureDate>2010-05-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
