As of 31 December 2017[update], the company had 444 million barrels of oil equivalent (2.72×109 GJ) of proved reserves, of which 58% was petroleum, 22% was natural gas, and 20% was and natural gas liquids and all of which were in the Permian Basin.

[2] In 2003, Energen Resources acquired 93 billion cubic feet of gas equivalent of proved reserves in the San Juan Basin of New Mexico and southern Colorado for $39 million.

[3] In 2004, Energen Resources acquired San Juan Basin coalbed methane properties from a private company for $273 million.

[4] In 2009, the company acquired assets in the Permian Basin from Range Resources for $182 million.

[6] In 2015, the company sold the majority of its assets in the San Juan Basin for $395 million.