JOINT FILING AGREEMENT
EXHIBIT A
The undersigned each agree that (i) the statement on Schedule 13D relating to the common units
representing limited partnership interests of Eagle Rock Energy Partners, L.P., a Delaware limited
partnership, has been adopted and filed on behalf of each of them, (ii) all future amendments to
such statement on Schedule 13D will, unless written notice to the contrary is delivered as
described below, be jointly filed on behalf of each of them, and (iii) the provisions of Rule
13d-1(k)(1) under the Securities Exchange Act of 1934 apply to each of them. This agreement may be
terminated with respect to the obligation to jointly file future amendments to such statement on
Schedule 13D as to any of the undersigned upon such person giving written notice thereof to each of
the other persons signatory hereto, at the principal office thereof.
Dated
May 3, 2007
| EAGLE ROCK HOLDINGS, L.P. By its general partner, Eagle Rock GP, L.L.C. |
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| By: | /s/ Xxxxxxx X. Xxxxx | |||
| Xxxxxxx X. Xxxxx | ||||
| Manager | ||||
| EAGLE ROCK GP, L.L.C. |
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| By: | /s/ Xxxxxxx X. Xxxxx | |||
| Xxxxxxx X. Xxxxx | ||||
| Manager | ||||
| MONTIERRA MINERALS & PRODUCTION, L.P.
By its general partner, Montierra Management LLC |
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| By: | /s/ Xxxxxx X. Xxxxx | |||
| Xxxxxx X. Xxxxx | ||||
| Chief Executive Officer | ||||
| MONTIERRA MANAGEMENT LLC |
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| By: | /s/ Xxxxxx X. Xxxxx | |||
| Xxxxxx X. Xxxxx | ||||
| Chief Executive Officer | ||||
| NATURAL GAS PARTNERS VII, L.P. |
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| By: | /s/ Xxxxxxx X. Xxxxx | |||
| Xxxxxxx X. Xxxxx | ||||
| Authorized Member | ||||
| NATURAL GAS PARTNERS VIII, L.P. |
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| By: | /s/ Xxxxxxx X. Xxxxx | |||
| Xxxxxxx X. Xxxxx | ||||
| Authorized Member | ||||
| NGP INCOME MANAGEMENT L.L.C. |
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| By: | /s/ Xxxx X. Xxxxx | |||
| Xxxx X. Xxxxx | ||||
| President | ||||
| NGP-VII INCOME
CO-INVESTMENT OPPORTUNITIES, L.P. By its general partner, NGP Income Management L.L.C. |
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| By: | /s/ Xxxx X. Xxxxx | |||
| Xxxx X. Xxxxx | ||||
| President | ||||
| NGP 2004 CO-INVESTMENT INCOME, L.P. By its general partner, NGP Income Management L.L.C. |
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| By: | /s/ Xxxx X. Xxxxx | |||
| Xxxx X. Xxxxx | ||||
| President | ||||
| NGP CO-INVESTMENT INCOME CAPITAL CORP. |
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| By: | /s/ Xxxx X. Xxxxx | |||
| Xxxx X. Xxxxx | ||||
| President | ||||
| /s/ Xxxxxxx X. Xxxxx | ||||
| Xxxxxxx X. Xxxxx | ||||
