As the cell reaction is between hydrogen and oxygen, the continuous supply of these gases is vital. oxygen poses no problem, as it is freely available from the air. The best way to provide hydrogen fuel has not yet been resolved Hydrogen reservoirs con- taining pressurised gas, or as liquid, have been con- sidered. One promising avenue seems to be the use of non-stoichiometric metal hydrides which can reversibly store hydrogen. In addition to this there is much work on using methane, methanol, petrol