Several months ago I posted on the issue of whether olive oil needs a hechsher.
The funny thing is that although it seems clear that no hechsher is needed for consuming olive oil, it is possible that for those that wish to be mehadeir to use olive oil for the menorah, a hechsher would be needed simply to determine that it is olive oil at all, and not some other ersatz substitute. On the other hand, it is also possible that the hechsher is based on a combination of fundamental, though possibly flawed, assumptions (that the tanker that is labeled Spanish Olive Oil is not really filbert oil from Turkey) and the din in Yoreh Deah that olive oil doesn't really need a hechsher at all, as I noted in the cited post.
So: the bottom line is:
Don't spend one cent more for special super duper shemen zayis zach extra virgin olive oil. You're just wasting your money. It's most likely isn't virgin, and it might not even be olive oil at all. And it is "super duper", in a manner of speaking. The duper is the merchant. You are the dupee. Buy store brand el cheapo oil-- just avoid pomace oil. It doesn't burn well.
I just returned from a week in Israel. On Shabbos, Rav Eisenstein of Maalot Dafna/Machal, gives a halacha shiur. This one was a diatribe on how wrong it is to use any but the most beautiful and expensive olive oils, zach kasis l'maor, Extra Virgin Olive oil. He said the whole point of Chanuka is to not be satisfied with "adequate" in Kiyum Hamitzvos, and to lazily and cheaply take the easy way out is an affront to the mussar haskeil of Chanuka.
I've been thinking about what Rav Eisenstein said. I think it falls into the "some things are worth believing even if they're not true" group. Here's what Wiki says about acidity in olive oil:
Extra-virgin olive oil Comes from virgin oil production only, and is of higher quality: among other things, it contains no more than 0.8% free acidity (see below), and is judged to have a superior taste, having some fruitiness and no defined sensory defects. Extra-virgin olive oil accounts for less than 10% of oil in many producing countries; the percentage is far higher in the Mediterranean countries (Greece: 80%, Italy: 65%, Spain 30%).Virgin olive oil Comes from virgin oil production only, but is of slightly lower quality, with free acidity of up to 1.5%, and is judged to have a good taste.
Refined olive oil is the olive oil obtained from virgin olive oils by refining methods that do not lead to alterations in the initial glyceridic structure. It has a free acidity, expressed as oleic acid, of not more than 0.3 grams per 100 grams (0.3%) and its other characteristics correspond to those fixed for this category in this standard. This is obtained by refining virgin olive oils with a high acidity level and/or organoleptic defects that are eliminated after refining. Note that no solvents have been used to extract the oil, but it has been refined with the use of charcoal and other chemical and physical filters. Oils labeled as Pure olive oil or Olive oil are primarily refined olive oil, with a small addition of virgin-production to give taste.
Olive pomace oil is refined pomace olive oil often blended with some virgin oil. It is fit for consumption, but may not be described simply as olive oil. It has a more neutral flavor than pure or virgin olive oil, making it unfashionable among connoisseurs; however, it has the same fat composition as regular olive oil, giving it the same health benefits. It also has a high smoke point, and thus is widely used in restaurants as well as home cooking in some countries.
The way I understand it, you could chemically reduce the acidity in every grade of oil to zero, so unless you trust the producer, you're wasting your money and being taken for fool. It would be nice to believe that a hechsher vouches for the character of the oil, but see the second sentence in this update.