The equilibrium concentrations of two ternary mixtures of methane, ethane and propane in the aqueous phase with gas hydrates were measured at pressures from 6 MPa to 20 MPa and temperatures from 274 K to 299 K at different salinity levels. These conditions for the gas mixtures selected were well inside the hydrate formation envelope so that the vapour phase could not coexist in equilibrium. A laboratory procedure was developed for the formation of homogeneous mixed hydrate crystals in the absence of a vapour phase. The compositional results generated in this work were compared against experimental data reported in the literature as well as against the predictions of the CSMGem thermodynamic model (Sloan and Koh, 2008; Ballard, 2002) [1,2]. (c) 2013 Elsevier Ltd. All rights reserved.