The link below details a second study made by UC Davis confirming their earlier study that the most popular national brands of olive oil fail sensory testing and the IOOC standards while at the same time passing the three traditional chemical tests for determining high quality olive oil. The earlier study was criticized by some large producers as being biased so for this study they took larger samples and had two labs accredited by the IOOC to do the analysis. The results were essentially the same as the results in the earlier study.

It is interesting that a human taste panel can still detect more defects caused by oxidation than the established chemical tests. This is why new tests are being developed, primarily by Australia and Germany, to be able to better detect oxidation in olive oil. The study also details the findings using these new methods of chemical anaysis. It is worth reading the entire study.

http://www.olivecenter.ucdavis.edu/report%20041211%20final%20reduced.pdf