The pyrolysis of oil shale to produce transportation fuels is a complex process. The organic matter in the oil shale is tightly bound with a heterogeneous mineral matrix. Several physical changes occur during the thermal conversion of kerogen in oil shale to produce hydrocarbon products. The creation of pore space during pyrolysis is an important physical process which determines the flow behavior of the pyrolysis products and the ultimate recovery. In this paper, we report the effect of temperature (350-500 degrees C) on oil shale pyrolysis and creation of pore volume during thermal treatment. One inch diameter oil shale cores from different depths of a single drill hole in the Uinta Basin were used. Increase in the pyrolysis temperature resulted in higher weight loss and a corresponding increase in the oil yield. Three-dimensional X-ray micro tomography (XMT) was performed to characterize and to analyze the nature of the pore network structure before and after pyrolysis. XMT scans of the cores at 42 mu m voxel resolution displayed distinguishable features of reaction products and source rock. Unconstrained pyrolysis of organic rich core produced large pore space during thermal treatment. The three-dimensional pore network structure was established with pores as large as 500 mu m developed after pyrolysis. Lattice Boltzmann simulation of flow through the developed pore network structure suggested that permeabilities from 173 Darcy to 2919 Darcy can be expected. (c) 2013 Elsevier Ltd. All rights reserved.