Class I and Class II behavior of the rock failure process under uniaxial compression has been numerically simulated using an elastoplastic cellular automaton (EPCA). A linear combination of stress and strain was used as the feedback signal to control the loading process in the numerical model. Uniaxial compressive simulations of heterogeneous rock failure were made using this control method and by considering different homogeneity indices and different linear combinations of parameters, as well as different yield criteria. The results indicate that Class II behavior can be numerically simulated in a complementary way to the laboratory testing method utilized in a servo-controlled testing machine. Whether the rock behaves in a Class I or Class 11 manner depends on the homogeneity of the rock sample, the linear combination parameters and the yield criterion selected. (c) 2006 Elsevier Ltd. All rights reserved.