A highly active superacid of 8 mass% Pt-supported ZrO2 for the skeletal isomerization of butane to isobutane is obtained by impregnating zirconia gel with 0.5 mol dm(-3) H2SO4 followed by drying, impregnating the sulfated gel with a solution of H2PtCl6, and finally calcining in air at 600 degrees C.