Your innocent little question could be the topic of an entire book - and, indeed, it is the topic of many. We are amazed to see how many books about olive oil are currently in print. Here is a sampling:

Soon olive oil books will be giving religion or sex books a run for their money.

The basics of olive oils are fairly simple, though. Olive oil is produced principally in Spain, Italy, France, Greece, Turkey Portugal, Tunisia, Morocco, and California. As with wine, the flavor can vary dramatically depending on the source, the variety of olive, the soil conditions, weather, etc. Some olive oils are "single-estate oils," that is, an oil from a single variety of olive. Others, including most Italian oils, are blends of oils from different types of olives and different countries.

Olive oil is pressed from the ripe olives after they are harvested. Oil from the first pressing is classified as virgin. Extra virgin simply means an oil from the first pressing that is particularly low in acid - less than 1%. It is considered the finest oil, and is likely to have the fruitiest and most pronounced flavor. Virgin olive oil may have as much as 4% acid. Fino or fine olive oil is a blend of extra virgin and virgin olive oils, with an acid content not above 3%.

After the first pressing, more oil is extracted in subsequent operations using a combination of pressure, heat, and chemical solvents. These refined oils may be blended with virgin oil to replace some of the flavor lost in the processing, and are sold as pure olive oil or just olive oil. In this country, you may also stumble upon light olive oil, which is not lower in calories, but which has been so finely filtered as to remove most of its color and fragrance (and flavor). It has a higher smoke point than the other types of olive oil, though, so it is well suited to high-temperature frying.

How many types of oil you keep on hand is simply a matter of preference. If you wanted to keep your list to two, we’d suggest an extra virgin for salads, marinades, serving with bread, and other uncooked uses, and a good-quality plain oil for low- to medium-temperature cooking. If you are willing to keep three olive oils active in your pantry, we’d add a bottle of light oil for high-temperature cooking.

Beyond that, the sky’s the limit, as you seek out and savor the differences between various nationalities, sources, and brands of oils.