This article proposes a new physically sound empirical equation for computing the K-values in reservoir fluids applications in a wide range of pressure and temperature. In order to examine the accuracy of the presented equation, its results for bubble pressure calculations were compared with the experimental data of 122 reservoir mixtures collected from literature. In addition, bubble pressure predictions of the new equation were compared with those of the state equations of Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) and three empirical equations, i.e. Whitson, Standing and Wilson. Compared to the experimental data, the average relative deviations of bubble pressure calculations for the proposed equation, PR, SRK, Whitson, Standing and Wilson were obtained 11%, 14%, 29%, 66%, 30% and 38% respectively. (C) 2012 Published by Elsevier Ltd.