Microbial communities present in the Gulf of Mexico rapidly responded to the Deepwater Horizon oil spill. In deep water plumes, these communities were initially dominated by members of Oceanospirillales, Colwellia, and Cycloclasticus. None of these groups were abundant in surface oil slick samples, and Colwellia was much more abundant in oil-degrading enrichment cultures incubated at 4 °C than at room temperature, suggesting that the colder temperatures at plume depth favored the development of these communities. These groups decreased in abundance after the well was capped in July, but the addition of hydrocarbons in laboratory incubations of deep waters from the Gulf of Mexico stimulated Colwellia's growth. Colwellia was the primary organism that incorporated (13)C from ethane and propane in stable isotope probing experiments, and given its abundance in environmental samples at the time that ethane and propane oxidation rates were high, it is likely that Colwellia was active in ethane and propane oxidation in situ. Colwellia also incorporated (13)C benzene, and Colwellia's abundance in crude oil enrichments without natural gas suggests that it has the ability to consume a wide range of hydrocarbon compounds or their degradation products. However, the fact that ethane and propane alone were capable of stimulating the growth of Colwellia, and to a lesser extent, Oceanospirillales, suggests that high natural gas content of this spill may have provided an advantage to these organisms.