A joint report from the National Oceanic and Atmospheric Administration, the Environmental Protection Agency and the Office of Science and Technology Policy found the level of dissolved oxygen near the site of the oil spill in the Gulf of Mexico was 20 percent less than average.
Scientists working on the report said microbes are using the oxygen as they consume subsurface oil left over from the spill.
Steve Murawski, a chief NOAA fisheries scientist and head of a joint scientific panel examining the oil spill, said the lower level of dissolved oxygen hasn't created a dead zone in the Gulf of Mexico.
"None of the dissolved oxygen readings have approached the levels associated with a dead zone and as the oil continues to diffuse and degrade, hypoxia (oxygen deprivation) becomes less of a threat," he said in a statement.
While scientists cautioned that they didn't "specifically" examine the link between the rate of oil biodegradation and dissolved oxygen, independent studies suggest there is a correlation.
The joint report said external studies suggest oxygen is being used when microbes consume the light components of oil in subsurface waters.