The initial fouling rates of four crude oils were determined at a nominal bulk temperature of 315C, an initial heated wall shear stress of 13 Pa, and initial surface temperatures between 375 and 445C. These initial fouling rates ranged from 1.3(10- 6) to 7.8(10- 5) m2 K/kJ. Corresponding Arrhenius plots were linear with the initial fouling rates passing through an isokinetic temperature of 407.5C. A plot of the natural logarithm of the pre-exponential factors [7.6(104)-5.2(1015) m2 K/kJ] versus the apparent activation energies (128-269 kJ/mol) was also linear, confirming the validity of the isokinetic temperature and the presence of the compensation effect. Below the isokinetic temperature, the relative fouling rates were Crude Oil C Crude Oil A Crude Oil D Crude Oil B; above the isokinetic temperature, the relative fouling rates were reversed (Crude Oil B Crude Oil D Crude Oil A Crude Oil C). Chemical characterization of a fouling deposit suggested that the dominant fouling mechanism at these conditions was coking, with significant contributions from sedimentation (iron sulfide) and corrosion ( 340 m/yr) of the 304 stainless steel test material.