A kinetic model was obtained for the Marlim crude vacuum residue (VR) hydroconversion. Marlim VR mixed with FCC decant oil in an 80%/ 20% weight basis was put in contact with a commercial NiMo on gamma-alumina catalyst in a stirred batch reactor. Several temperatures and oil/catalyst ratios were used over different times (0-240 min), at a 110 bar pressure and constant hydrogen flow. The analysis of the collected product showed residua conversions of up to 70%. Hydroconversion kinetics involving thermal and catalytic cracking contributions was proposed to represent the obtained data. The resulting system of differential equations of the kinetic model was solved within reaction time, taking into account the experimental temperature profile. The chi-square objective function was minimized to adjust model parameters. A proposed effective hybrid minimization method was used, by applying a Newton-type method between certain simulated annealing minimization steps. The proposed kinetic model allowed the representation of thermal and catalytic cracking effects, in order to take into account different catalyst concentrations. Therefore it is possible to consider distinct reactor hydrodynamics, such as expanded or bubble column reactors. (c) 2005 Elsevier B.V. All rights reserved.