Experimental results for the various phase equilibria of {(1 - x)CH4 + xCH(3)(CH2)(18)CH3} are presented. (Vapour + liquid) equilibria were measured for 26 different mixtures covering almost the whole composition range. The temperature varied between 303 K and 370 K. (Solid + liquid) and (solid + vapour) equilibrium measurements were performed for 20 different mixtures. The pressures applied did not exceed 100 MPa. On the basis of the primary experimental two-phase equilibrium results, the course of the three-phase curve (solid eicosane + liquid + vapour) could be derived. The second critical endpoint, where solid eicosane is in equilibrium with a critical fluid phase (s(C20) + 1 = g), was found at a temperature T = (307.37 +/- 0.15) K, a pressure p = (89.0 + 0.25) MPa, and a mole fraction in the critical fluid phase of x = (0.049 +/- 0.0012).