WASHINGTON (AP) - A new federal report says microbes that are gobbling up oil from the BP spill haven't caused problems with oxygen loss in the Gulf of Mexico.

Federal officials say some underwater oxygen levels have fallen by 20 percent, but the levels aren't low enough to create 'dead zones.' They say that's good news because it shows the microbes are working, but aren't causing oxygen loss.

Steve Murawski (MOO-row-ski), the scientist who headed the federal research team, said that means efforts to control the oil with dispersants hit the "sweet spot" they were aiming for.

Scientists worried that if microbes had eaten too much, it would deplete the oxygen in deep water, choking fish. But more than 400 tests show that the oxygen levels weren't dangerously low.