In his book Extra Virginity, Tom Mueller explains why you can't believe everything you read on olive oil labels. Much of the "extra-virgin" olive oil sold in the U.S. has actually been mixed with lower-priced, lower-grade oils and artificial coloring, he says.

Choosing good oil:

• Find a store where you can taste olive oils before you buy them, and where the staff acan answer a few basic questions about how, where and by whom they were made.
  Some good stores:
  Olive Press, Sonoma, CA
  Amphora Nueva, Berkeley, CA
  Eataly, Manhattan, NY
• If you can't taste it, choose a stor that performs stringent quality control in its production and selection of oils, such as The olive Press, Zingerman's, Beyond the Olive, or Corti Brothers.
• Unlike many wines, which improve with age, extra virgin olive oil is perishable: like all natural fruit juices, its flavor and aroma begin to deteriorate within a few months of milling.
  Buy as close to the mill as possible.
  Buy from a seller who purchases excellent oil in bulk.
  Buy from olive oil purveyors that store their bottled oil in a cool, dark warehouse and have high turnover.
• Buy in quantities you can use up quickly.
• Prefer dark glass bottles.
• Store away from light, heat and oxygen.
• Don't pay much attention to the color of an oil.
• Buy only extra virgin - other categories, pure, light, ... have gone thru chemical refinement which takes away flavors and heathy benefits.
• Choose oils that smell and taste vibrant and lively.
  Don't be put off by bitterness or pungency - these are usually indicators of the presence of healthful antioxidants.
• Look for bottles with "best buy" dates.
• Unfiltered oil and filtration: Some consumers view unfiltered olive oil, with tiny bits of olive pulp and skin floating in it, as more authentic and flavorful. Improper or excessive filtration can attenuate certain flavors and aromas, and most makers of fine oil prefer simply to rack their fresh-pressed oil repeatedly, removing sediment, rather than to filter it. Other top oil-makers swear by filtration, which can significantly increase an oil's shelf life. In either case, be on the lookout for a layer of sediment at the bottom of the bottle, which often soils faster than the oil itself, and can produce the tast flaw of muddy sediment.
• Certain terms commonly used on olive oil labels are anachronistic, and sometimes indicate that the producer is paying more attention to the image of an oil than to what's actually inside the bottle. Take the terms "first pressed" and "cold pressed," for example. Since most extra virgin oil nowadays is made with centrifuges, it isn't "pressed" at all, and all true extra virgin oil comes exclusively form the first processing of the olive paste. EU (European Union) regulations state that "cold pressed" can be used only when the olive paste is kept at or below 27° C during the malaxing process, a level respected by nearly all serious producers - and when the oil is actually extracted with a press, not a centrifuge.
• Pick a powerful oil - variously described as "robust", "early harvest," or "full-bodied" - to accompany foods with strong or distintive flavors, fett'unta (garlic bread) or to drizzle over vinilla ice cream (yes ice cream).
  Choose a milder oil - often called "mild," "delicate fruit," or "late harvest" - for foods like fish, chicken or potatoes.
• Frying -
  Extra virgin olive oil is fine for sauteing and shallow frying,
  Refined olive oil is probably a better choice for deep-fat frying, but there are many light extra virgin oils that hold up well to frying.
  The lower an oil's free fatty acidy (FFA), the higher its smoke point (the temperature at which it begins to smoke and produce unpleasant, unhealthy byproducts,) and the more times it can be reused.

Books:
Extra Virginity: The Sublime and Scandalous World of Olive Oil, Tom Mueller 2012
  Review of Extra Virginity at NPR

Links:
Extra Virginity | Truth in Olive Oil
Extra Virgin Olive Oil, Balsamic Vinegars & Olive Oil Gifts, Sonoma & Napa CA, The Olive Press
www.beyondtheolive.com olivecenter.ucdavis.edu www.oliveoilsource.com www.modernolives.com.au www.oliveoil.com www.super-premium-olive-oil.com www.aromadictionary.com/EVOO_blog/ naooa.org www.cooc.com