Isobutane is self-alkylated to an alkylate composition having high octane components including trimethylpentanes in the presence of a solid catalyst and a minor amount of a C.sub.5 and higher olefin. The self-alkylation process utilizes a chlorided alumina catalyst having from about 4 to 15 weight percent chlorine. The olefins of choice employed in the isobutane self-alkylation reaction are isoolefins having 6 or 7 carbons. The isobutane may be derived from the isomerization of n-butane and the isomerization process may be integrated with the self-alkylation process.