A hydrocarbon feed is isomerized in liquid phase in the presence of a metal halide catalyst, a hydrogen halide solvent and hydrogen at a temperature ranging from at least 50.degree.C and not greater than the critical temperature of the mixture of the hydrocarbon feed and the hydrogen halide. The partial pressure of the hydrocarbon feed-hydrogen halide mixture is maintained to be at least equal to the critical pressure of the hydrocarbon feed and not greater than the critical pressure of the mixture of the hydrocarbon feed and the hydrogen halide. The molar ratio of the hydrogen halide to the hydrocarbon feed is at least 1:1 and the molar ratio of hydrogen halide to metal halide catalyst ranges from about 10:1 to about 40:1. The preferred catalyst is aluminum chloride or aluminum bromide. The preferred solvent is hydrogen chloride or hydrogen bromide.