This reminds me of a program I saw on TV once where a guy over in Europe had some sort of contraption to turn sheep manure into methane gas. He claimed that methane burns at a higher percentage rate than gasoline, thereby producing more power and fuel economy. From what I've read, an automobile does not burn 100% of the gasoline put into it. Some of it remains unburned and passes through to the atmosphere, where methane burns nearly 100%.
Talk about a renewable resource!
The downside is, I would guess that it smells like neither french fries nor peanut butter.