The thermodynamics of polyolefins in reaction mixtures is of considerable interest because sorption and diffusion in growing polymer particles strongly affect polymerization rate, copolymer composition, and subsequent product degassing. The thermodynamics of polyethylene (PE)/hydrocarbon systems related to gas-phase polymerization was extensively studied and described in the literature. However, such data are not yet available for PE-liquid penetrant systems related to slurry polymerization. Hence, we developed a simple methodology for investigating the solubility of liquid penetrants in polymer samples. Common diluents (n-octane, n-hexane, n-pentane) were sorbed in PE samples of varying density from 902 to 967 kg m(-3). Equilibrium solubilities were obtained by extrapolation from the drying data using the initial slope method. The dependence of liquid n-hexane solubility in PE on temperature (in the range 25-68 degrees C) is the principal outcome of our measurements. Comprehensive measurements provide a unique set of thermodynamic data useful especially for slurry olefin polymerizations.