The flow of rheologically complex materials (e.g. shear-thinning fluids) through complex pore structures is a fundamental process in many industrial applications, yet is poorly understood. To this end we apply 3D lattice Boltzmann simulation techniques to provide a pore-scale description of such flow processes. Simulation results are compared directly to corresponding spatially resolved magnetic resonance imaging velocimetry data, providing an extremely stringent and thorough check on the accuracy of the simulation methodology. Excellent agreement is produced for a range of shear-thinning fluids. Heterogeneity in the flow field was observed to increase as the fluids became more shear-thinning, and is quantified. (C) 2007 Elsevier B.V. All rights reserved.