Bulk olive oil buyers around the country are forced to answer this question for themselves as they’re procuring oil. Depending on your intended use for the oil and who you ask, you’ll find many different answers.
In the manufacturing realm, the intended use for olive oil is most often an ingredient. It goes into a final product and slight differences in taste and color are usually undetectable. The grade of olive oil is the biggest factor that affects taste and color. So, if the quality and grade is similar across a few different countries of origin, it’s likely that more than one variety could work for you.
If your manufacturing standards will allow it, be flexible. Choosing a country of origin where this year’s production level is high can help save money. For example, as production in Spain dropped in 2013, Spanish olive oil became more expensive. Other countries that experienced increased production over that harvest-- for example, Turkey and Tunisia-- had slightly lower prices. Being willing to change your country of origin can save you money, especially if you’re only looking for an ingredient and a low cost is a priority for you.
In the gourmet or food service realm, you may be looking for a specific source for your olive oil. For example, if you are a food service company selling to Spanish restaurants, they will know if you stop carrying a product of Spain-- customers often grow accustomed to a particular country’s flavor and olive varietal blend. In this case, it would be important to maintain consistent Spanish inventory, even if you have to pay more. To secure a specific origin and low price, ask for an annual or semi-annual contract for your volumes.