Understanding the nature of heavy organic compounds and the mechanisms of their depositions is essential with the increased utilization of deeper reservoirs (heavier asphaltic crude) and miscible flooding techniques for recovery of oil. To prevent asphaltene deposition in different places, it is necessary to predict the onset and the amount of deposition due to various factors. This research tries to understand the physical phenomenon of asphaltene deposition within the reservoir and around a producing well. An experimental setup was developed to observe the physical phenomenon of asphaltene deposition. Experimental runs contained simultaneously flowing oil and solvent into a saturated solvent medium. The pore size and the pore size distribution of the used porous mediums were also measured. The experiments were performed at constant injection rate of 30 cm3/hr and system temperature of 90 aC. The concentration of n-heptane varied from zero (fresh oil) to 40, 50, 60, and 80 volume percent. Crude oil from Ahwaz oil field, one of the Iranian oil fields, which had an asphaltene content of approximately 13%, was selected for this study. The change in pressures for mixtures of 40 and 50 volume percent of n-heptane were completely different with those of 60 and 80 volume percent. It seemed that they followed different mechanisms. The time required to reach complete plugging decreased dramatically with increasing concentration. At higher concentrations, the plugging occurred very rapidly. At concentration values below 0.965%, complete plugging took place after a long period of time, depending on the value of concentration. For the investigated crude oil, the amount of precipitated asphaltene increased with concentration of n-heptane. The precipitated asphaltene reached its maximum value almost immediately after contact between oil and precipitant. Longer contact times had no effect on the mechanism of precipitation.