This makes very good sense, if it’s practical to recycle the used cooking oil. It’s greener to use bio-diesel than petroleum-based diesel a fuel source, as burning bio-diesel apparently produces less net carbon dioxide. It’s definitely an option as an alternative fuel source. However once the production of bio-diesel involves clearing more land, particularly the rainforests which serve as major carbon dioxide sink, then it’s probably not that green anymore. The best way is still to cut down energy consumption and recycle whenever possible.