The solubility of small molecules and their mixtures in polyethylene is studied using a recently proposedunited atom force field. By comparing the simulation results with experimental data on solubility of smallmolecules in semicrystalline polyethylene, it is found that crystallinity can severely effect the solubility of asolute, especially if it is highly soluble in the polymer of interest. It is also observed that small moleculesform aggregates within the polymer in the liquid phase.