Deposition of complex and heavy organic compounds which exist in petroleum crude can cause a number of severe problems. To prevent deposition inside the reservoir, in the well head, and inside the transmission lines it is necessary to be able to predict the onset and amount of deposition due to various factors. In the present paper the basic mechanisms of organic deposition are described based on two different microscopic theories; and their predictive capabilities are discussed. These models are the continuous thermodynamic (CT) model and the steric colloidal (SC)model. Utilization of kinetic theory of aggregation enables one to develop a fractal aggregation (FA) model which combines the ideas of the two proposed CT and SC models. The FA model is capable of describing several situations, such as the phenomena of organic deposition, growing mechanism of heavy organic aggregates, the geometrical aspects of aggregates, the size distributions of precipitated organics, and the solubility of heavy organics in an oil under the influence of miscible solvents.