WASHINGTON — Ten months after the nation's largest biodiesel plant opened on the coast of Washington state, its owners are facing the same financial pressures that have brought a once high-flying industry down to earth.

Imperium Renewables Inc., has delayed a $345 million initial public offering, put on hold its plans for four additional plants, and trimmed its corporate staff. Its chief executive officer resigned without explanation.

The $78 million plant on the Pacific coast is still operating, even though prices of soybean oil and other vegetable oils have jumped 100 percent to 200 percent in the past year. Hopes to buy much of the feedstock from eastern Washington farmers never blossomed and, instead, the plant is using mostly canola oil from Canada.

And while biodiesel was supposed to help reduce Americans' dependence on foreign oil and cut greenhouse gas emissions, the domestic market has not materialized as expected. Virtually all of Imperium's product is being shipped to Europe.

"We are experiencing challenging times," said John Plaza, Imperium's founder and CEO. "The entire industry is facing this."

Ever the entrepreneur, Plaza isn't about to give up. His latest venture, with the help of Boeing, is to develop and manufacture green aviation fuel.

A Virgin Atlantic 747 that flew from London to Amsterdam in February was partially powered by a biofuel produced by Imperium. It was the first such flight by a commercial airline. One of the plane's engines was powered by a mixture of kerosene, babassu oil and coconut oil. Babassu oil, from the nuts of the babassu tree, which grows in the Amazon region of South America, and coconut oil are often used in cosmetics.

"It's a hot topic out of necessity," Plaza said, adding that the green aviation fuel could be cheaper than the Jet A fuel now used and could reduce carbon dioxide emissions from jet engines by 80 percent. Airplanes could start flying regularly on biofuel within three to five years, and the Grays Harbor plant could be modified to produce it, Plaza said.

Pilots on the Virgin Atlantic flight said they noticed no drop in performance in the engine running on biofuels. Mechanics later found the engine had not been affected, said Terrance Scott, a Boeing spokesman.

"This is not about rhetoric, this is about finding a biofuel," said Scott. "We are looking for something that will offset fuel costs and burn cleaner."

Burning one pound of jet fuel now releases 3.1 pounds of carbon dioxide, Scott said. According to an Environmental Protection Agency report, aircraft currently account for about 3 percent of U.S. carbon dioxide emissions. Some scientists estimate that unless changes are made, carbon emissions from aircraft will triple globally by 2050.

Both Airbus, Boeing's main competitor, and the U.S. Air Force are working on developing biofuel. Possible sources include switchgrass, algae and jatropha, a scrub bush that grows on marginal farmlands.

"It won't be a simple, cheap process," Plaza said of developing green aviation fuel.