PURPOSE: To obtain a method for alkylation of isoalkane with olefins using a sulfonated polymer catalyst and a catalytic composition.

CONSTITUTION: Isoalkanes are alkylated using olefins in the presence of a sulfonated macroporous cross-linked vinyl arom. polymer and a sulfonated carbon absorbent polymer, which hava a water content less than about 1.0% by weight and a surface area more than about 400 m2/g. It is useful to synthesize branched alkanes used for high-octane gasoline in high selectivity and high conversion rate, e.g. in the synthesis of trimethylpentane from isobutane and butene.