On April 20, 2010, the Deepwater Horizon offshore drilling unit exploded as the result of a blowout, damaging the Macondo 252 well southeast of the Louisiana coast and causing substantial amounts of oil and gas to leak into the ocean. In order to determine the effects of the oil spill on Gulf of Mexico waters, a research expedition was conducted from July 12-20, 2010 on board the R/V Cape Hatteras. The goals of this expedition were to study and map plumes of natural gas emanating from the wellhead, and to determine if microbially mediated hydrocarbon consumption in these plumes is leading to oxygen depletion. Water samples were collected from the area surrounding the wellhead while water current speeds were recorded with Acoustic Doppler Current Profiling (ADCP). Dissolved methane, ethane and propane concentrations were determined by use of gas chromatography and rates of microbial methane oxidation were measured by a radiotracer method, utilizing 3H-CH4. Additionally, the extent of microbial consumption of methane, ethane and propane is being investigated using stable carbon isotopic signatures of these gases, measured by isotope ratio mass spectrometry. Contoured depth profiles of dissolved gases and methane oxidation rates were generated, and show two distinct deep water plumes with elevated dissolved hydrocarbon concentrations, with methane concentrations reaching a maximum of 180000 nM, and increased rates of microbially mediated methane consumption. Preliminary analyses indicate that a large portion of the observed oxygen depletion in the same depth range as the hydrocarbon plume can be attributed to hydrocarbon consumption.