Spatially uniform avalanche discharges of relatively long duration have been obtained in a UV‐preionized, high‐pressure, rare‐gas–halide laser. In the case of XeCl pulse durations as long as 70 ns have been observed. The spatial distribution of the small‐signal gain in a plane transverse to the laser axis has been measured. The active discharge cross sections with better than 90% gain uniformity were 2.8×3.0 and 2.8×2.5 cm2for XeCl and KrF, respectively. The use of neon rather than helium as a buffer gas increased the discharge cross section, and the laser pulse duration resulting in improved laser output energy densities of 4.5 J/l in XeCl and 2.8 J/l in KrF.