How long past the "Use by date" is cooking oil good for if it has never been opened?
It depends on how the oil has been stored. Light causes oil to oxidize and go rancid. If the oil is stored in a cool, dark place it will last much longer. The true test is simply to smell the oil. If it has any off aromas, don't use it. Neutral oils like vegetable or canola oil shouldn't really have a smell at all because they are deodorized during processing.