Take a walk down the olive oil section of any major supermarket - you'll see olive oils branded as 'Extra Virgin', 'Virgin', 'Light' and just plain old 'olive oil' or 'pure' olive oil.
So, what does it all mean (and how can something be 'extra' virgin anyway)?
Extra Virgin olive oil - this is the highest grade of olive oil. It is made by crushing olives and extracting the juice of fresh, healthy olives mechanically, without the use of chemicals or excessive heat. It meets rigorous standards, including having low acidity (not more than 0.8 grams per 100 grams) as well as having no taste 'defects'. It is the only cooking oil that is made without the use of chemicals and industrial refining.
Virgin olive oil - this is the second highest grade of olive oil. It is made in the same way as Extra Virgin olive oil but may have modest taste defects and/or lower chemical parameters, such as an acidity level of between 0.8 and 2 grams per 100 grams. How does an oil go from being Extra Virgin to Virgin? Usually the difference is caused by a number of factors, including growing conditions; the length of time from harvest to processing (causing acidity levels to rise); or it may just be flaws in the processing method (for example, too much contact with air causing oxidation).
'Pure' / standard olive oil - made from a blend of refined and virgin oils. Refined oil comes from treating low quality or defective virgin olive oil with the use of charcoal or other chemical and physical filters, such as solvents and high heat to extract as much oil as possible and neutralise the taste. This allows producers to use olives of lower quality and to blend from a wide variety of sources.
'Light' olive oil - don't be confused by this one, it's not light in calories, just light in flavour. It is made from 'pure' or standard olive oil that has been selected for its neutral taste.
So, what does it all mean? If you have come to the same conclusion as me, Extra Virgin is the way to go. Plus, you don't need to worry about having multiple types of oil in the pantry to suit different cooking needs - Extra Virgin comes in a wide range of flavours and intensity depending on the olive type. For example, a Frantoio oil will give you a fragrant, peppery finish, while a Pendolino oil will give a more subtle flavour suited to a wider range of palates and uses, including baking.
If you're interested in reading more, the Australian Olive Association has produced a diagram that simply demonstrates how an olive goes from being on the tree to becoming an oil of a particular grade.