Fusion energy, when it becomes available, will practically be a source of unlimited amount of energy. For example, just a kilogram of D-T fuel would release 108 kWh of energy (3.39´1011 J per gram) and would provide the requirements of a 1GW (electrical) power station for a day. Deuterium is contained naturally in water, one D atom out of 6700 H atoms and can be separated out. Tritium is unstable by nature, with a half-life of 12.3 years, and has to be manufactured from lithium. In a reactor, once the initial start-up inventory of tritium (manufactured elsewhere) has been used up, tritium can be obtained by neutron bombardment lithium contained in the blanket. Lithium is widely distributed throughout the earth’s crust. Fusion will consume very small quantities of these fuels, 0.5-5 tonnes per GW(e).a, depending on the efficiency of using the natural lithium. The total reserves of lithium are estimated  to be 1016 Gigajoules in land, and 1019 Gigajoules in the sea, sufficient for thirty thousand, and thirty million years respectively, at today’s energy consumption rate. Figure 1 shows the comparison of D-T fuel with respective amounts of fossil and fission fuels that produce the same amounts of energy.