Does cooking oil evaporate?
Volatile oils will evaporate in a few days or weeks, "fixed" oils are more resistant to evaporation. Most vegetable cooking oils are classified as fixed oils. However, if you set out a container of most cooking oils, it would partially evaporate very slowly over months to years leaving a sticky varnish. You can see this varnish on the sides of pots and baking pans where the process has been speeded up by heat.