The vapour pressure of binary mixtures of hydrogen sulphide with ethane, propane, and n-butane was measured at T = 182.33 K covering most of the composition range. The excess Gibbs free energy of these mixtures has been derived from the measurements made. For the equimolar mixtures G(m)(E) (x(1) = 0.5) = (835.5 +/- 5.8) J (.) mol(-1) for (H2S + C2H6), (820.1 +/- 2.4) J (.) mol(-1) for (H2S + C3H8), and (818.6 +/-0.9) J (.) mol(-1) for (H2S + n-C4H10). The binary mixtures of H2S with ethane and with propane exhibit azeotropes, but that with n-butane does not. (c) 2006 Elsevier Ltd. All rights reserved.