The critical temperatures and pressures of four binary mixtures (2-methylpropane + 1-butene, 2,2,4-trimethylpentane + 2-methylpropane, 2-methylpropane + methane, and 2-methylpropane + carbon dioxide) and four ternary mixtures (2-methylpropane + 1-butene + methane, 2-methylpropane + 2,2,4-trimethylpentane + methane, 2-methylpropane + 1-butene + carbon dioxide, and 2-methylpropane + 2,2,4-trimethylpentane + carbon dioxide) were measured using a high-pressure view cell. On the basis of that, the dependences of the critical properties of the reacting mixture in the alkylation of 2-methylpropane with 1-butene in the presence of a solvent methane or carbon dioxide upon the initial ratio of 2-methylpropane/1-butene, amounts of methane or carbon dioxide added, and reaction extent were estimated.