In this work, the alkylation of isobutane and butene, catalyzed by sulfuric acid in the presence of the fluoride-containing ionic liquids [Bmim][PF6] and [Bmim][SbF6], was investigated. The use of the binary mixture catalysts brought to a higher C-8 selectivity and longer catalyst lifetime, compared with the results obtained when working with sulfuric acid only. This was attributed to the formation of new species when [Bmim][PF6] or [Bmim][SbF6] are added to sulfuric acid. The acidolysis of [Bmim][PF6] and [Bmim][SbF6] was accompanied by the release of hydrogen fluoride (HF) and the decomposition of anions to [PF6-x-2y(HSO4)(x)(SO4)(y)](-) and [SbF6-x-2y(HSO4)(x)(SO4)(y)](-), respectively. The presence of these new species after acidolysis was measured and confirmed by ion chromatography, H-1-Nuclear Magnetic Resonance (NMR), F-19-NMR and P-31-NMR. The production of HF and the complexation of anions and carbenium ions both play an important role in stabilizing the carbenium ion and improving the catalytic performance.