NEW ORLEANS/WASHINGTON, (Reuters) – A U.S. judge yesterday blocked the Obama administration’s ban on deepwater  drilling, complicating its efforts to improve the safety of  offshore oil operations after the worst spill in U.S. history.

The White House said it would immediately appeal the  judge’s ruling, issued in New Orleans. Oil companies involved  in offshore drilling operations had challenged the government’s  six-month moratorium.

A new Reuters/Ipsos poll found that most Americans still  support offshore drilling, despite watching a huge slick from  BP Plc’s Gulf of Mexico oil spill devastate fragile wetlands  and communities along the U.S. Gulf coast.

The possible scale of the ecological catastrophe was  underscored when U.S. scientists said as much as one million  times the normal level of methane gas has been found in some  regions near the spill, enough to deplete oxygen and create a  dead zone.

If such dead zones were linked to the spill they could  ultimately add to BP’s mounting costs.

The 64-day-old disaster has shattered investor confidence  in BP, which has seen its stock price slashed in half since the  start of the crisis. The British energy giant’s London share  price tumbled to its lowest level in 13 years on Tuesday.

After the BP well ruptured on April 20, spewing millions of  gallons of crude, President Barack Obama imposed the ban on  deepsea drilling while officials checked that other wells were  operating safely.

In granting a request by more than a dozen oil services  companies for the ban to be overturned, Judge Martin Feldman  challenged its “immense scope.”

The Interior Department, which oversees offshore drilling,  said despite the ruling, the firms still had to meet new safety  and environmental rules before they could resume operations.

Expanding offshore drilling was among Obama’s proposals to  revamp U.S. energy policy. He hoped it would generate support  from Republicans for more controversial aspects of his plans to  fight climate change.

But he shelved that plan after the spill and White House  spokesman Robert Gibbs said Obama believed that “continuing to  drill at these depths without knowing what happened does not  make any sense.” The administration will probably ask for a  stay of the court ruling as it pursues its appeal.

The court’s decision was a victory for offshore energy  producers like BP, Chevron Corp and Royal Dutch Shell. They  have been hamstrung by the ban, and are considering relocating  their giant rigs to other basins like Brazil.

Shares in oil drilling companies briefly spiked after the  ruling but dipped again when the Obama administration said it  would appeal. The S&P energy sector fell 1.3 percent.