The stabilization and extension of operation of XeCl (308 nm) and KrCl (222 nm) excimer lasers by the addition of very low concentrations of hydrogen gas is described. Lifetime extension of a sealed-off XeCl laser operating at 8 W and 150 Hz is reported, with more than three million shots to half power. Spectroscopic analysis of the laser gas indicates a large reduction in a discharge-induced absorption feature below 230 nm; no absorption is observed at 308 nm.