How do you clean oil off walls?

There are a number of ways to do this depending upon the size of the stain, as well as the type of wall. If for example the wall is paint on plaster, then an oil based cleaner will work Excellently. In lue of a good oil based cleaner, then gasoline will even work. If the wall is made of something like concrete or metal, then shot blasing techniques such as sand blasting may be the best option.