NEW YORK — BP is probably sturdy enough to survive the worst oil spill in U.S. history. But investors are shaving billions of dollars off its value with every day that crude gushes into the Gulf of Mexico.

Yesterday alone, the first trading day since BP's latest attempt at a fix failed, and the day the government announced it had opened a criminal probe into the disaster, its stock took a hit of 15 percent.

The British oil giant is worth $75 billion less on the open market than it was when the Deepwater Horizon rig exploded six weeks ago. Other companies involved in the spill — Transocean, Halliburton and Cameron — have all lost at least 30 percent in value.

And as oil seeps unchecked into the Gulf, nearby states, businesses, environmental regulators and injured workers and cleanup crews are eyeing damages that could total billions more.

"This will be the mother of all liability claims," said Fred Kuffler, a Philadelphia maritime lawyer who has handled oil-spill lawsuits.

The stakes were raised yesterday as Attorney General Eric Holder said federal authorities had opened criminal and civil investigations into the spill. He did not specify which companies or individuals might be targets.

BP says it has spent $1 billion so far on fighting and cleaning the spill. Its liabilities and potential fines are growing by the day, and it could be August before the company gets control of the situation by completing two relief wells.

The company has already agreed to pick up the government's cleanup tab and any "legitimate" damage claims. BP said yesterday it has paid out about $40 million to cover about half of the 30,000 claims it has received.

At least 130 lawsuits have been filed seeking damages for business lost from the spill. Most are from seafood processing plants, charter boat captains, hotels, restaurants and others who make their living from the sea or from coastal tourism.

Based on federal law, BP and partners Anadarko Petroleum and Mitsui & Co. also face a minimum fine of $1,000 per barrel of oil spilled, said Eric Schaeffer, who led the Environmental Protection Agency's enforcement office from 1997 to 2002. Schaeffer is now the director of the Environmental Integrity Project.

The government estimates 20 million to 43 million gallons of crude have gushed into the Gulf over the past six weeks. If the spill were contained today, the fines would add up to between $480 million and $1 billion.

Already, the Gulf disaster has eclipsed the 1989 Exxon Valdez spill, which, after two decades of lawsuits, cost Exxon Mobil $4.5 billion. That's roughly $654 per gallon in today's dollars, according to Blake Fernandez, an analyst with Howard Weil, an energy investment firm with headquarters in New Orleans.

Experts are increasingly looking at the Valdez disaster as a conservative model because the Gulf Coast is home to far more people and businesses than Alaska, where the Valdez ran aground.

In addition to cleanup costs, the government will probably also ask BP to pay for restoring an oil-soaked coastline — including repairs to sensitive marshlands, oyster beds and fisheries, Kuffler said.

Doug Inkley, a senior scientist for the National Wildlife Federation who monitored the Gulf spill from a boat, said the damage is nearly impossible to fix.

Crews could try to burn marshlands to get rid of the oil, or they could send people in with rags to try to mop it up by hand.

But both solutions could do more damage than help, Inkley said.

What's especially troublesome to many scientists is BP's use of chemicals to disperse the crude plumes. They argue that the dispersants could harm fish larvae and other creatures living below the surface.

BP also will face claims from commercial fishermen, hotels, party boat operators, and other businesses that depend on the Gulf Coast.

Then there are contract workers helping with the cleanup who say they have suffered respiratory problems because of exposure to the oil.

BP is self-insured, and analysts say it has enough money to pay for the growing calamity without putting the company at risk of bankruptcy.