The pressure-volume-temperature (PVT) dependencies of four molten polystyrenes (PS) were determined at T = 450-530 K, and P = 0.1 - 190 MPa. In addition, five sets of published PVT data for PS were examined. The Simha-Somcynsky (S-S) lattice-hole equation of state (eos) was used to analyze the data. Fitting the data to eos yielded the characteristic reducing parameters, viz. P*, V*, T*, where from the Lennard-Jones measures of energetic (epsilon*), and volumetric (nu*) interactions were calculated. It was found that: (I) the values of the interaction parameters for PS resins varied, viz. 27.7 <= epsilon* <= 35.2, and 35.5 <= nu* <= 50.2; (2) epsilon* was dependent on v*, and (3) epsilon* and nu* linearly increased with the logarithm of molecular weight. In addition, these volume-averaged interaction parameters depend on the chain configuration, as well as the presence of additives. (c) 2005 Elsevier Ltd. All rights reserved.