The effect of benzene or thiophene addition to the feed on the rates of coke formation during naphtha pyrolysis has been investigated in a jet‐stirred reactor at atmospheric pressure in the temperature range of 1073‐1103 K. In addition, the effect of temperature, space time, weight ratio of steam to naphtha and the material of construction on the rate of coke deposition was also studied. The rate of coke formation increased as the temperature, space time and aromatic content of the feed was increased whereas it decreased with an increase in the weight ratio of steam to naphtha or the thiophene content of the feed. Addition of thiophene increased the rate of naphtha pyrolysis and significantly reduced the aromatic yields. Rates of coke formation for both thiophene‐free and thiophene‐containing naphtha could be modeled by power law expressions involving the aromatics.