A three-dimensional combustion cell was used to investigate experimentally the effect of reservoir heterogeneities on the in-situ combustion process. Four experiments were conducted to study the combustion process within specially prepared unconsolidated sand packs saturated with water and a medium-heavy 930 kg/m(3) (20.7 degrees API) crude oil. One experiment was performed using a homogeneous sand pack as a base case against which the results of the other experiments might be compared. In another experiment, the sand pack was prepared with a thin, high-permeability streak running horizontally through the mid-plane of the sand pack. In the other two experiments, the matrix consisted of two sand pack layers of the same thickness but of different properties. One of these latter two experiments was conducted with the more-permeable layer above the less-permeable layer, while the other was conducted with the layers reversed. It was found that the presence of the single high-permeability streak significantly reduced the total amount of oil recovered, while the volumetric sweep efficiency was highest for the dual layer sand pack in which the more-permeable layer was the lower of the two layers. This was probably because the channelling of the gas into the lower layer is partially countered by the gas override mechanism.