The kinetics of asphaltene conversion was studied during the hydrotreating of Maya heavy crude oil. Experimental tests were conducted in a pilot plant at the following reaction conditions: total pressure of 70-100 kg/cm(2), liquid hourly space-velocity (LHSV) of 0.33-1.5 h(-1), and reaction temperature of 380-420 degrees C at a constant hydrogen-to-oil ratio of 5000 ft(3)/bbl. A commercial NiMo/Al2O3 catalyst was used in all experiments. Asphaltenes were precipitated from Maya crude and from hydrotreated products in a Parr Batch Reactor at 25 kg/cm(2) and 60 degrees C with n-heptane as solvent. Asphaltene hydrocracking data were used to estimate reaction orders and activation energy using a power-law model, and the average absolute error between experimental and calculated concentrations of asphaltenes was found to be less than 5%. (c) 2005 Elsevier B.V. All rights reserved.