The Mishnah says that oil from the town of Tekoa is the highest-ranked oil. Oil from this place should be used for Menachot (meal offerings). Abba Shaul says the second-ranked oil is oil from Regev, which is in Jordan. All lands were really valid for bringing olive oil for the Menachot, but people usually bring it from the top-ranked places over here, either Tekoa or Regev, because they wanted to serve Hashem with the best-produced oil.
You should not bring oil from an olive tree that grew in a field that needs fertilization, nor from a field that requires irrigation, nor from a field that has seeds planted between the trees, because these types of olive trees are poor quality. The seeds planted between them grab much of the water that's needed. But if a person brings oil for Menachot from one of these sources, the oil is Kasher (valid). These fields where the trees grow are lacking in something, and we're nervous that the trees didn't get what they need. Therefore, the oil from the olives on these trees is going to be of inferior quality. We're nervous, though, so you shouldn't bring it; but if you brought it, it's still considered to be Kasher.
You should not bring oil from Anpikinon, meaning unripe olives. These types of olives are less than one-third of their full growth, and the oil is bitter. If you did bring this type of oil, it's considered not valid. You should not bring oil from olives that were soaked in water. If you have an olive that fell off a tree prematurely, in order to extract oil from it at some point, it has to first be soaked in water. This is a lower type of oil because the water it's soaked in destroys the olive. Not from pickled olives or from boiled olives. They also don't produce a quality oil. If a person did bring oil from these types of olives, the Minchah (meal offering) is not valid.