Washington ? Government scientists studying the BP disaster are reporting the best possible outcome: Microbes are consuming the oil in the Gulf without depleting the oxygen in the water and creating “dead zones” where fish cannot survive.

Outside scientists said this so far vindicates the difficult and much-debated decision by BP and the government to use massive amounts of chemical dispersants deep underwater to break up the oil before it reached the surface.

Oxygen levels in some places where the BP oil spilled are down by 20 percent, but that is not nearly low enough to create dead zones, according to the 95-page report released Tuesday.

In an unusual move, BP released 771,000 gallons of chemical dispersant about a mile deep, right at the spewing wellhead instead of on the surface, to break down the oil into tiny droplets.

The idea was to make it easier for oil-eating microbes to do their job. But the risk was that the microbes would use up the oxygen in the water. So BP had to perform a delicate balancing act.

“Has it hit the sweet spot? Yes. Was it by design? Partly,” said Steve Murawski, the National Oceanic and Atmospheric Administration senior scientist who headed the federal team of researchers.

One reason that oxygen levels didn’t drop too low was the natural mixing of water in the Gulf, which kept bringing in oxygen from other areas, Murawski said. Oxygen levels would have had to fall by three-quarters for the water to be classified as a dead zone, he said.

The Gulf of Mexico already has a yearly major problem with a natural dead zone — this year, it is the size of Massachusetts — because of farm runoff coming down the Mississippi River. Fertilizer in the runoff stimulates the runaway growth of algae, depleting the oxygen in a giant patch of the Gulf every summer.

Federal officials had been tracking oxygen levels and use of dispersants since the spill, which spewed more than 200 million gallons of oil into the Gulf between April and July. Had the oxygen plummeted near dangerous levels, the dispersant use would have been stopped, said Greg Wilson, science adviser at the Environmental Protection Agency’s emergency management office.