Polar and surface active additives are usually added to lubricating oils to provide desired functional properties. Generally, additive selection is based on a trial-and-error procedure and no fundamental molecular understanding is available, especially when a mixture of additives is used. The goal of this research is to develop a molecular thermodynamic model for the action of polar components in a hydrocarbon media, used as a lubricant. This exploratory program is designed to determine the applicability of a thermodynamic model to tribology. The model will incorporate the interaction among different additive chemistries. The initial model will be checked experimentally with a few simple additives.