A study of the (difluoromethane + water) system was conducted at temperatures between (255 and 298) K. and pressures from (0.06 to 1.30) MPa. The solubility of difluoromethane in liquid water was measured from (280 to 298) K. at pressures up to the hydrate formation pressure. The (p, T) behavior of the (liquid + hydrate + vapor) three-phase equilibrium was measured from (274 to 292) K. The (p, T) behavior of the (ice + hydrate + vapor) three-phase equilibrium was measured from (257 to 273) K. Solubility-corrected enthalpies of dissociation were determined at the lower quadruple point (Q1) using the Clapeyron equation. The de Forcrand method was used to determine the hydration number of the hydrate at Q1. The results show that not all of the cages in the SI hydrate structure are filled. (C) 2011 Elsevier Ltd. All rights reserved.