(I) Apart from hydroelectricity, there are several other non-depletable energy sources in use such as wind turbines and solar heating. (II) However, it is only in relatively few circumstances that any of them prove to be economic. (Ill) In fact, the developing countries account for one-fourth of the world's production and one-fifth of the world's consumption of commercial energy. (IV) Even where they appear to be operating as ordinary commercial ventures, they are usually heavily subsidized. (V) So, at present, oil, natural gas and coal are still the major suppliers of energy in the world