One of the end-products of anaerobic decay is biogas, which is produced naturally from decay under water or in the guts of animals, and artificially in airtight digestion. Itodo and Phillips described biogas as “a methane-rich gas that is produced from the anaerobic digestion of organic materials in a biological-engineering structure called the digester”. This definition suggests that biogas is only produced artificially, but this is not the case. It is believed that the scope of their definition may perhaps have been limited by their comparison of artificial production-processes, thus ignoring the natural occurrence of biogas. However, Itodo and Phillips are not alone in this way of defining biogas. GEMET [5] states that biogas is “gas rich in methane, which is produced by the fermentation of animal dung, human sewage or crop residues in an air-tight container”.