I assume that you mean cooking oil. Rancid oil looks cloudy and / or lumpy, may not smell too bad but depending on how rancid it has gone food cooked in it won't taste great.
Oil can be OK but look rancid if water has been allowed to get into the bottle. Either way it's not taking the risk, bin it and buy a new bottle.
It may seem a good money saving idea to buy a big bottle but if you don't use it that often your better off buying a smaller bottle that you will use with in a couple of months, so you are then cooking with fresher oil.