The diffusion coefficient and the physical solubility of isobutene and trans-2-butene in aqueous sulfuric acid solutions cannot be determined experimentally due to the occurrence of fast chemical reactions. In the present contribution these physicochemical parameters are estimated. For the solubility an isobutane−isobutene analogy is applied for the range 0−100% H2SO4. A correlation technique, initially proposed by Rudakov et al.,11 was used for describing the experimental data at low acid concentrations and for estimation purposes for more concentrated solutions. Diffusion coefficients for inert gases in electrolyte solutions were measured using a modified diaphragm cell. It was found for CO2 and N2O in KCl solutions that the diffusion coefficient is not a function of the ionic strength of the electrolyte solution and therefore not a function of the activity coefficient of the diffusing component. It appears that the correlation Dη0.6 = constant holds up to 80 mass % sulfuric acid, as is the case for several other aqueous electrolyte solutions. Diffusion coefficients for butenes in sulfuric acid solutions (up to 96 mass %) are estimated from CO2 coefficients in these solutions.