Olive oil, once used in the U.S. mostly by immigrants from Mediterranean countries and adventurous gourmets, is now mainstream. In 2007, Americans consumed over 70 million gallons; a nearly ten-fold increase since 1982.

This is good news, as olive oil has the highest percentage of heart-healthy monounsaturated fat of any edible oil, and quality brands contain abundant antioxidants, substances that have been shown to provide cardiovascular and anti-cancer effects.

When choosing olive oil, I recommend buying small bottles of certified organic extra-virgin olive oil. Check the label for the ICEA (Istituto per la Certificazione Etica e Ambientale, which means Ethical and Environmental Certification Institute) logo, and that of another organic certification body such as the USDA's green-and-white ORGANIC logo. Quality extra-virgin olive oil should have a natural peppery finish and a deep, "green" aroma
of grass and artichoke. Such oils are not cheap, because they rely on careful cultivation that preserves olive oils legendary taste and health benefits. But the reward is more than worth it.

From: http://www.drweilblog.com/home/2010/9/14/choosing-olive-oil.html