Liquid-vapour and fluid-solid phase transitions were experimentally determined under pressure on the system methane + a ternary waxy mixture using a full visibility cell. The wax was an approximately equimolar mixture of n-C-16, n-C-17 and n-C-18, the composition being chosen to obtain a mixture with an average molecular weight similar to heptadecane. Measurements were performed according to the synthetic method on different mixtures ranging from 0 to 99.5 mol% of methane. The liquid-solid phase transitions were investigated up to 100 MPa and fluid phase boundary was studied in the temperature domain from 293 to 373 K. Measurements performed on this pseudo-binary system were compared to the phase diagram of the binary system methane + heptadecane. (C) 2010 Elsevier B.V. All rights reserved.