It's not a viable alternative. Do you have any idea of how much oil we actually use?

As of 2000, the United States was producing in excess of 2.9 billion gallons of waste vegetable oil annually, mainly from industrial deep fryers in potato processing plants, snack food factories and fast food restaurants. If all those 2.9 billion gallons could be collected and used to replace the energetically equivalent amount of petroleum, almost 1% of US oil consumption could be offset.