The knowledge of activity coefficients at infinite dilution (gamma(infinity)) are of particular importance for the synthesis, design, and optimization of separation processes because the largest separation effort is required to remove the last traces of impurities. Furthermore, reliable gamma(infinity) values are required to select selective solvents (entrainers) for separation processes such as extractive distillation, extraction, and so forth or to check far separation problems (azeotropic points and miscibility gaps). Various experimental techniques for the determination of limiting activity coefficients in pure solvents have been developed. In this paper gamma(infinity) values for different hydrocarbons (n-hexane, cyclohexane, 1-hexene, and benzene) for NMP-water mixtures measured with the help of the dilutor technique in the temperature range between 30 and 60 degrees C are reported, which can be used to select and to optimize the selectivity and capacity for the separation of aliphatics from aromatic or alkanes from alkenes using NMP/water mixtures as the entrainer.