The agreement was announced Thursday by the Houston-based companies.
Vanguard Natural Resources will also assume $140 million of debt from Eagle Rock Energy Partners, which will become a wholly-owned indirect subsidiary.
The agreement requires approval of the boards of both companies.
Vanguard Natural Resources deals in acquisition, production and development of oil and natural gas properties. The company has operations in Texas, Wyoming, Arkansas, Oklahoma, New Mexico, Montana, Colorado, Louisiana, Mississippi and North Dakota.
Eagle Rock Energy Partners is also involved with oil and natural gas properties.