MARTINEZ, Calif. — Later this fall, Tom Powers will harvest his olives and press them into his Alhambra Valley brand authentic extra virgin olive oil with a distinctive peppery finish.

"This is really high quality stuff," says Powers, whose two varieties of Tuscan olives grow amid the dry, rolling hills of Contra Costa County, northeast of San Francisco.

But Powers and other California growers worry that shoppers will never know what sets their product apart because of what they allege to be widespread mislabeling in the olive oil industry. So they are petitioning the federal government to adopt the same familiar terms used by European producers: extra virgin, virgin, etc.

Oil produced in Spain, Italy and other Mediterranean countries is classified under the international standards, but the U.S. has never adopted them. Instead, the U.S. Department of Agriculture uses a 1948 classification system that defines olive oil as fancy, choice, standard or substandard.

Because the term carries no regulatory weight in this country, unscrupulous producers here and abroad can get away with branding olive oil bound for U.S. grocery shelves as extra virgin — the highest and most expensive grade — even if it's of lesser quality.

"Producers who mislabel their olive oil as extra virgin can say, 'What do you mean it's not extra virgin?' because the term hasn't been defined," said Bruce Golino, a board member of the California Olive Oil Council, an industry group.

The council petitioned the USDA in 2004 to replace its outmoded classification system, and the agency expects to solicit public input by the end of this year, according to a spokesman. A final decision will come after that.

"When people go into a retail store and buy a gallon of extra virgin olive oil for $12, they should question whether that's really extra virgin," said grower Don Della Nina, 59, who sells a 375-milliliter bottle of his own, California-grown Olio Bello d'Olivo-branded oil for $14.

California growers also have an ulterior motive for adopting the international standards: They hope eliminating cheap international competition will help the state's producers increase their share of a U.S. market still dominated by European countries.

Officials with the Spanish, French, Italian and Greek olive oil industry organizations didn't immediately return requests for comment via telephone and e-mail.

The push for new standards comes at a time when olive oil production and consumption in the United States is on the rise. U.S. sales have doubled in the last decade as Americans look for healthier food options, and olive oil now accounts for about a third of all cooking oils used at home.

California is far and away the leading U.S. producer. Olive oil production here rose from about 250,000 gallons in 2001-2002 to about 400,000 gallons in 2004-2005. Production here is expected to roughly double over the next three years, said Paul Vossen, who studies olive oil at the University of California Cooperative Extension office in Sonoma County.

Among olive oils, extra virgin is king. To earn the classification under the international standards, the fruit must be picked before it becomes too ripe, and pressed soon thereafter without solvents, heat or intense pressure, according to Golino. It must meet strict requirements for acidity.

The powerful taste of extra virgin reflects the distinctive flavor and aroma of the olives. It is also believed to have greater health benefits than lesser quality oils.

Some instances of fraud involve lower-grade oils classified as extra virgin, but in the most egregious examples, cheaper vegetable oils are sold as extra virgin olive oil.

Last February, federal officials seized more than 20,000 gallons of oil from a warehouse in New Jersey. Though some of it was labeled extra virgin, it was actually soybean oil, according to the Food and Drug Administration. Olive oil is five to six times more expensive than soybean oil, according to the FDA.

The council wants the USDA to test olive oil for adulteration and to set up a taste panel, which may be the only way to distinguish refined olive oil from extra virgin. The USDA would not be able to punish producers found to be violating the standards, but the California Olive Oil Council says the threat of lawsuits from competitors would pressure companies to comply.

"Right now," council president Alan Greene said, "there is a feeling that a lot of the oil labeled extra virgin on retail store shelves is in fact a lower grade."