Alkylation of isobutane with butene (C-4 cut from an industrial alkylation feed) was catalysed by a class of strongly acidic ionic liquids. A dramatic enhancement of the catalytic effect was observed for the ionic liquids containing the SbF6- anion. The optimal alkylate was obtained using the acidic ionic liquid [HMIm][SbF6] (47.9 wt.%)/CF3SO3H (52.1 wt.%) as the catalyst. The C-8 selectivity was as high as 80% and the research octane number (RON) was 95. These results were better than those obtained by using either neat H2SO4 or CF3SO3H as the catalyst. (C) 2012 Elsevier B.V. All rights reserved.