The key process variables in an alkylation unit are reaction temperature, acid strength, isobutane concentration, and olefin space velocity. Reaction temperature and acid strength affect product quality, with lower temperatures and appropriate acid strengths producing higher quality alkylate. Isobutane concentration is generally expressed as the isobutane to olefin ratio, with higher ratios increasing octane number and yield. Olefin space velocity also affects product quality, with lower velocities increasing octane number. Sulfuric acid and hydrofluoric acid are the primary catalysts used. Olefins and isobutane are the main feedstocks.