Alkylation of 1-butene with isobutane is employed industrially to produce C8 alkylates (such as trimethylpentane) as high-octane motor fuel. Such alkylates supply roughly up to 15% of the U.S. gasoline pool. However, the process uses large quantities of sulfuric acid (as catalyst) generating acid waste whose handling poses health and environmental hazards. The main pollutants are sulfur dioxide (SO2) emissions (which causes acid rain) and acid leakage in the alkylation unit. This chapter presents an alternate process that uses a solid catalyst (Nafion® supported on silica) in dense CO2 media to produce C8 alkylates (solid acid/CO2 process). Although the environmental concerns with SO2 emissions and acid leakage are eliminated, the activity of the solid acid catalyst is lower than sulfuric acid resulting in an approximately 30% higher capital investment than the conventional process. For C8 alkylate productivity, capital investments and operating costs to be nearly identical, the required olefin throughput in the solid acid/CO2 process must be four-fold higher. Such analyses establish performance targets for the solid acid/CO2 process to be commercially viable.