(Reuters) - As much as 1 million times the normal level of methane gas has been found in some regions near the Gulf of Mexico oil spill, enough to potentially deplete oxygen and create a dead zone, U.S. scientists said on Tuesday.

Texas A&M University oceanography professor John Kessler, just back from a 10-day research expedition near the BP Plc oil spill in the gulf, says methane gas levels in some areas are "astonishingly high."

Kessler's crew took measurements of both surface and deep water within a 5-mile (8 kilometer) radius of BP's broken wellhead.

"There is an incredible amount of methane in there," Kessler told reporters in a telephone briefing.

In some areas, the crew of 12 scientists found concentrations that were 100,000 times higher than normal.

"We saw them approach a million times above background concentrations" in some areas, Kessler said.

The scientists were looking for signs that the methane gas had depleted levels of oxygen dissolved in the water needed to sustain marine life.

"At some locations, we saw depletions of up to 30 percent of oxygen based on its natural concentration in the waters. At other places, we saw no depletion of oxygen in the waters. We need to determine why that is," he told the briefing.

Methane occurs naturally in sea water, but high concentrations can encourage the growth of microbes that gobble up oxygen needed by marine life.

Kessler said oxygen depletions have not reached a critical level yet, but the oil is still spilling into the Gulf, now at a rate of as much as 60,000 barrels a day, according to U.S. government estimates.

"What is it going to look like two months down the road, six months down the road, two years down the road?" he asked.

Methane, a natural gas, dissolves in seawater and some scientists think measuring methane could give a more accurate picture of the extent of the oil spill.

Kessler said his team has taken those measurements, and is hoping to have an estimate soon.

"Give us about a week and we should have some preliminary numbers on that," he said