SAN FRANCISCO -- Many of the olive oils lining supermarket shelves in the United States are not the top-grade extra-virgin oils their labels proclaim, according to a report from the University of California, Davis.

Researchers analyzed popular brands and found 69 percent of imported oils and 10 percent of domestic oils sampled did not meet the international standards that define the pure, cold-pressed, olive oils that deserve the extra-virgin title.

"Consumers, retailers and regulators should really start asking questions," said Dan Flynn, executive director of UC Davis' Olive Oil Center, which conducted the study in partnership with the Australian Oils Research Laboratory, in South Wales.

Funding for the study came in part from California olive oil producers and the California Olive Oil Council, a trade group that works to promote locally produced oils.

Although the survey's sample size was relatively small and selected at random - 19 widely distributed brands purchased from retailers in San Francisco Bay Area, Sacramento and Los Angeles - the study held the claims on their labels to a scientifically verifiable standard, said Flynn.

The results came as the U.S. Department of Agriculture prepares to adopted scientifically verifiable standards for nomenclature such as "virgin" or "extra virgin," in an effort to clear up concerns about labeling accuracy. The standards will be implemented in October, and are similar to those upheld by the International Olive Council.

The "extra-virgin" designation indicates that the oil was extracted without the use of heat or chemicals, is pure, satisfies a taste test and falls within chemical parameters established by the IOC.

The United States is the world's third-largest consumer of olive oil, 99 percent of which comes from foreign producers.

The North American Olive Oil Association, which represents most olive oil importers, has conducted its own tests for years on the products it imports, and found problems with only one percent of samples, said its president, Bob Bauer.

He also questioned the objectivity of a study financed in part by California olive oil producers.

"The research was done by academics, but with funds supplied by the industry," Bauer said. "When you look at results that are so different from ours, it does raise some questions."

The head of the Olive Oil Chemistry and Standardization Unit at the International Olive Council, based in Spain, was not available for comment.

The study found that olive oil from Whole Foods, the country's largest organic food retailer, failed to meet two of the nine chemical parameters established for extra-virgin olive oil by the IOC. The company said it had not reviewed the study, but that it stands behind their 365 Everyday Value 100 percent Italian Extra-Virgin Olive Oil.

Whole Foods' supplier performs independent tests meant to ensure the oil "meets our requirements and the industry standards for extra-virgin olive oil," said spokeswoman Jennifer Marples.

There have long been questions about the quality of some of the olive oil being sold as extra virgin, said Flynn.

Olive oil production is labor intensive and costly. Poor quality oils can be made from olives that are too ripe or damaged. Extra-virgin olive oil is also fragile - it is susceptible to oxidation and degradation of its aromatic compounds due to aging, or to exposure to high temperatures and light.

The delicate nature of the production has led to adulteration, where extra-virgin olive oil was blended with cheaper, refined olive oil, or with seed or nut oils.

The discovery of altered oils in the 1990s led the European Union, which produces much of the world's supply, to create an investigative task force to look into the matter.

The results of the survey weren't surprising to Ruth Mercurio, who owns and runs We Olive, a California chain of stores specializing in olive oil.

"It's sad for consumers that there is fraud out there," said Mercurio, who has trained in-house tasters to help verify the quality of their product. "It's a problem, and maybe this will get folks to perk up and listen."