A fuel composition for fuel cells includes a polar solvent such as water, a first portion of a first fuel dissolved in the solvent at a saturated concentration, and a second portion of the first fuel suspended in the solvent to serve as a reservoir of fuel as the dissolved portion is consumed. Preferably, the first fuel is a hydride such as NaBH4. Optionally, the fuel composition also includes a second fuel such as an alcohol that also controls the solubility of the first fuel in the solvent, inhibits decomposition of the first fuel and stabilizes the suspension. Preferably, the fuel composition also includes an additive such as an alkali for stabilizing the first fuel.