From a 2011 UC Davis* report on extra-virgin olive oil sold in California:
http://olivecenter.ucdavis.edu/research/files/report041211fi...
>Of the five top-selling imported “extra virgin” olive oil brands in the United States, 73 percent of the samples failed the IOC sensory standards for extra virgin olive oils analyzed by two IOC-accredited sensory panels. The failure rate ranged from a high of 94 percent to a low of 56 percent depending on the brand and the panel. None of the Australian and California samples failed both sensory panels, while 11 percent of the top-selling premium Italian brand samples failed the two panels. Sensory defects are indicators that these samples are oxidized, of poor quality, and/or adulterated with cheaper refined oils.
*"We are grateful to Corto Olive, California Olive Ranch, and the California Olive Oil Council for their financial support of this research."