 Olives that are gently harvested while they are still very green and then processed within a few days or even a few hours, that's going to yield the best oil. So most important is looking for a label that says extra virgin olive oil, EVOO. That means it's cold pressed only once without heat or chemical solvents, and that's going to help it retain its nutrients. Finally, keep your oil in a cool, dark place and eat it or cook it as soon as possible.