Natural gas in various forms comprised approximately 2/3 of the hydrocarbons emitted from the Deepwater Horizon well blowout. Methane is believed to compose an estimated 87.5% of that natural gas. Sampling in June 2010 found no microbial breakdown of methane. [See http://www.sciencemag.org/content/330/6001/208.] Some estimates were that it would take decades for the methane to be decomposed.
Seeking to quantify the rate of degradation, researchers sampled at more than 200 sites between mid-August 2010 and the beginning of October 2010. They found exceptionally low methane in the Gulf waters, and no BP-related methane. In support of their conclusion that degradation had occurred, the researchers pointed to the following facts: (a) a huge drawdown in dissolved oxygen, which methane-munching bacteria (methanotrophs) would have consumed, and (b) the disappearance of almost all of the methane, ethane, and propane and some of the hydrocarbons in oil. Further, the researchers noted that they saw almost no methanotrophs in plume zones in June 2010, but many methanotrophs and other oil-degrading species in their subsequent sampling.
Critics argue that the plumes are very localized and mobile, and that the researchers simply lost track of where the plumes were located.
Related research papers can be found at http://www.sciencemag.org/content/330/6001/201.abstract and http://www.sciencemag.org/content/330/6001/204.abstract.