The basis of bioenergetics on Earth is briefly analysed. There are four types of energy supply (1) heterotrophy, (2) chemi-autotrophy, (3) bacterial photosynthesis and (4) plant photosynthesis. The main energy carrier is ATP. There are in addition many other classes of high-energy compounds such as amidine-, acyl-, carbamyl-, and enol-phosphates, acylthioesters, acyl-imidazoles, and onium compounds. Still other compounds can be envisaged. Taking these processes as a starting point, several possible modifications are suggested. Bioenergetics now centres around radiant and chemical bond energy. In other conditions other forms of energy for life processes are possible (electrical, mechanical, thermal, etc.). Guanine is a serious alternative to adenine, and, perhaps less likely but not negligible, other stable purine-derivatives. Several other compounds, such as porphin, isoalloxazines, etc., are very stable and are excellent candidates as alternate energy carriers. Free pyrophosphate and metaphosphate are alternatives to ATP.