As stated elsewhere at Ochef, olive oil is a vegetable oil.

Actually, now that we think about it, what vegetable oil is really made from a vegetable? Corn is really a fruit, a soybean is really a legume, a Canola is a made-up name for a modified and trademarked rapeseed variant, a sunflower seed is a seed, a safflower seed is a seed. And an olive is also really a fruit.

So technically and from the point of the devil’s advocate you have NO vegetable oil at all – never have, probably never will.

Getting back to your question, depending on what you are cooking and depending on the strength of the olive oil you have, you may be successful in substituting it. You can certainly do it – olive oil has the same oily properties and characteristics of other oils. It has a different smoke point than some other oils, but it has the same number of calories, and will provide the same “mouth feel” (a phrase we always feel compelled to put in quotation marks).

It really comes down to flavor. You can use a delicate olive oil, even a delicate extra virgin olive oil, in most recipes, and it’s very trendy to use all olive oil now. But a strong, peppery olive oil will not be an improvement in many recipes. If that’s all you have on hand, and if the oil plays a prominent role in whatever you are making, it may be better to hold off until you have a more plain vegetable oil or a more plain olive oil on hand.