| (1)   | The      Report fully complies with the requirements of Section 13(a) of the      Securities Exchange Act of 1934;and |
|-----------------|-----------------------------------------------------------------------------------------------------------------------|

| (2)   | The      information contained in the Report fairly presents, in all material      respects, the financial condition and results of operations of the      Registrant. |
|-----------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

|                      /s/ W.      Randall      Fowler                                                            |   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------|
|  Name:   W.      Randall Fowler                                                                                                                                                                                                                                                                                                                                                                                                                 |   |
|  Title:     Chief      Financial Officer of DEP Holdings, LLC,                                                                                                                                                                                                                                                                                                                                                                        |   |
|                     the General Partner of Duncan Energy Partners L.P.                                                                                                                                                                                                                                                                                                                        |   |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                |   |
|  Date:     March      1, 2010                                                                                                                                                                                                                                                                                                                                                                                                         |   |

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