How do you remove oil-based paint from fabric?

If it is a fresh canvas and it has some oil paint on it, then you can either paint over it with more oil paint or take off the canvas and restretch some new canvas over the supports. Oil over oil, oil over water, but NO water over oil. White Gesso, which you can buy at any art store covers a canvas very well, but is meant for priming canvas and is water based, it will not work over oil.