Hydrogen isotherms have been measured for the Pd0.98Al0.02, Pd0.96Al0.04, and Pd0.0.94Al0.06 alloys in the temperature range from 393 to 523 K. From these equilibrium data, the standard partial thermodynamic parameters at infinite dilution of H, ΔHH∘ and ΔSH∘, have been determined; the former becomes slightly more positive and the latter more negative, with increase of atom fraction Al, XAl.H diffusion parameters have been determined from the permeability of H through Pd–Al alloy membranes (393–523 K). DH* decreases and ED* increases with increase of XAl while the pre-exponential factors, DH∘,*, do not change significantly where the asterisk refers to conditions of infinite dilution of H. The dependence of DH and ED on H content have been determined for several of the Pd–Al alloys and the former decreases and the latter increases with H content. Similar data have been determined for the ternary alloys, (Pd0.77Ag0.23)0.98Al0.02 and (Pd0.77Ag0.23)0.96Al0.04 alloys.