Calado, J.C.G. and Streett, W.B., 1979. Liquid-vapor equilibrium in the system H2Ar at temperatures from 83 to 141 K and pressures to 52 MPa. Fluid Phase Equilibria, 2: 275-282. Experimental measurements of liquid-vapor phase equilibria in the system H2Ar are reported for thirteen temperatures in the range 83.09 to 141.42 K, and pressures to 52 MPa. The mixture critical line and the pressure-temperature trace of the three-phase line solid-liquid-gas have been located. These lines intersect at T = 84.0 K and P = 52.5 MPa to form an upper critical end point. The pressure-temperature trace of the three-phase line has a temperature minimum at T {reversed tilde equals} 82.5 K, P {reversed tilde equals} 20 MPa. © 1979.