Oil is a painting medium that uses oil (typically linseed oil) as the binder for the pigment. Oil by far has been the most preferred medium for painters throughout the centuries. Acrylic is gaining ground. One of the reasons that oil is so popular is that it stays moist for a long time. This allows the artist to work and rework a composition. It also makes glazing much more effective. The most common type of surface for an oil painting is canvas.