A raw material or feed stock should be renewable rather than depleting whenever technically and economically practicable. This is one of ''the 12 principles of green chemistry. A typical depleting raw material is petroleum. Today, almost all organic compounds come from petroleum: it was reported that 98% of the organic material in use comes from petroleum. It has been warned that petroleum resources could be exhausted in this century. Alternative resources for organic materials must be found that are renewable rather than depleting. Green chemistry recommends crops or biomass as alternative renewable resources.