How to check whether the Olive oil is fit for consumption or not? How to check whether the Olive oil is fit for consumption or not?
The oil is in a bottle and doesn't have any froth.

EDIT 1:

The oil is about 1 and a half years old. I kept it in a capped bottle. I didn't do anything to the oil. Haven't eaten it for quite a long time now.

Adding references to the answers will be more helpful.
Olive oil doesn't suddenly go rancid (unlike butter in which this process is pretty quick), but its taste deteriorates with time.  AFAIK it happens primarily due to oxidation, not bacteria or fungi, and there are no dangerous/poisonous byproducts.

I have a bottle of olive oil which I opened about a year ago and it tastes noticeably different from fresh oil (not too pungent to throw it out though).