A novel alkylation catalyst is described which is used in processes for alkylating olefin hydrocarbons with isoparaffin hydrocarbons to produce high octane alkylate products suitable for use as a blending component of gasoline motor fuel. The novel catalyst comprises a mixture of a hydrogen halide and a sulfone. The novel alkylation catalyst is utilized in a novel process for alkylating olefin hydrocarbons with isoparaffin hydrocarbons.