Due to the temperature dependence of the covolume created by the use o
f Sandler-Wong mixing rules, thermodynamically inconsistent results wi
ll be predicted at very high pressures, including the prediction of ne
gative heat capacities. In this paper, we propose a simple modificatio
n to the mixing rule, which prevents this problem and which performs s
lightly better in the prediction of the Gibbs excess energy. Published
by Elsevier Science Ltd.