In order to tell the difference between different types of olive oil, you must first know the different types and what they are made of:

• Extra-virgin olive oil comes from virgin oil production only, contains no more than 1.0% acidity, and is judged to have a superior taste. Extra Virgin olive oil accounts for less than 10% of oil in many producing countries. It is used on salads, added at the table to soups and stews and for dipping.
• Virgin olive oil comes from virgin oil production only, has an acidity less than 2%, and is judged to have a good taste.
• Olive oil is a blend of virgin and refined production oil, of no more than 1.5% acidity. It commonly lacks a strong flavor.
• Olive pomace oil is refined pomace olive oil often blended with some virgin oil. It is fit for consumption, but may not be described simply as olive oil. It has a more neutral flavor than pure or virgin olive oil, making it unfashionable among connoisseurs; however, it has the same fat composition as regular olive oil, rendering it the same health benefits. It also has a high smoke point, and thus is widely used in restauraunts as well as home cooking in some countries.

Extra Virgin olive oil and virgin olive oil is of course the choice to make if you are buying for domestic use on your food. Its flavor is strong and slightly bitter if fresh. Its colours range from green/yellow to green

In the U.S.A. the term "extra virgin olive oil" could be used on the label of any olive oil. New standards for grades of olive oil have been introduced and are in effect from 25 October 2010. The term "extra virgin olive oil" can now only be used on the label of products meeting certain criteria. They can be found here.