A dramatic cargo ship accident off the Alaskan coast last month highlighted a hard-to-track risk of doing business overseas: Problems at sea can result in big losses for companies relying on the products on board.

For Japanese automaker Mazda, last month's incident could mean the loss of nearly 4,800 cars and trucks headed for Canada and the United States. Although that's only a sliver of Mazda's annual sales, if the cars are damaged, there could be a shortage of some of its more popular models.

No one agency tracks how much cargo is lost at sea around the world each year. But because ships can carry such large loads, accidents take on a large scale. One sunken ship can carry thousands of cars worth tens of millions of dollars.

Industry experts estimate that anywhere from 2,000 to 10,000 containers fall off ships each year, less than 1 percent of the number of containers sent by sea annually but representing a huge cost to those who lose cargo to the ocean. The loss of even one shipping container, which can be 20 feet to 40 feet long and 8 feet high and may hold millions of small parts, could shut down a manufacturing line.

"What we've always struggled with is, how do you quantify that for someone?" said Nicholas Dewhurst, executive vice president for Boothroyd Dewhurst, a firm that helps companies develop cost-efficient product design. "The chances of you losing something aren't very great. But when you do, it's a huge cost. It may be the only one of something in the world, and now you can't get it back. It's sitting on the bottom of the ocean, and you've missed your market opportunity."

In late July, a car-carrying ship originating from Singapore had an almost-"Poseidon Adventure" experience: As crew members on the Cougar Ace adjusted the ballast waters in the ship's hull — something they needed to do before entering U.S. waters — the ship lost stability and listed 60 degrees on its side. The 23 crew members all were rescued. But the listing was so severe that a member of the salvage team looking into how to save the ship died Sunday when he slid down at least 80 feet and hit his head.

About half the cars on board are the compact Mazda3, which had a 16.4 percent sales jump in July. Dealers are already contending with a short supply of the car, averaging 21 days' worth of the vehicle, compared with an industry average of 60 to 70 days.

Before leaving the ship, the salvage crew determined that cars on two out of 14 floors were still chained in place, according to the U.S. Coast Guard. Greg Beuerman, a spokesman for Mitsui O.S.K., the ship's owner, said the cars were securely latched down. "From what we know right now, we are encouraged about the condition of the cars," he said.

Still, one of those decks has taken on water. Salvagers could begin pumping water off that deck today. They're also trying to determine how to get the ship to port. The cars, which are insured by Mazda and remain Mazda's property, were headed to Vancouver, British Columbia; Tacoma, Wash.; and then Los Angeles.

It wasn't the first dramatic cargo-ship accident this year. In March, an explosion on the Hyundai Fortune container ship as it was sailing through the Gulf of Aden from Asia to Europe damaged hundreds of containers. Insurers estimate its cargo was worth $225 million to $700 million.

Pirates also are a threat to cargo ships. Increased law enforcement in hot spots such as the Malacca Straits linking the Indian and Pacific oceans resulted in an overall decline in pirate attacks from 329 in 2004 to 275 in 2005, according to the International Maritime Bureau Piracy Reporting Center. But officials now worry that pirates are pairing up with terrorists.

Many companies don't like to admit they've lost cargo at sea. For one thing, there's a fear that environmentalists will target companies for the damage lost cargo could have on sea life. Curt Ebbesmeyer, an oceanographer in Seattle who tracks ocean debris to study patterns of currents, said Nike, Lego and The First Years toy company have been upfront about cargo losses, helping him develop intricate maps of otherwise elusive currents.