Solution gas liberation is one of the key factors contributing to the success in solution gas drive in heavy oil reservoirs. Unconsolidated sands dilate with decreasing effective stress, and contract with increasing effective stress. This paper describes special experiments that were designed to investigate the effect of sand matrix deformation on bubble nucleation and growth in heavy oil, and oil production. The experiments involved flow of heavy oil with dissolved gas in reconstituted sand packs. Gas bubbles were allowed to nucleate and grow in dilated sand packs by lowering the effective confining stresses in an undrained (closed) system. Then, oil was produced from the sand packs by reducing pressure. Production rates from these experiments were compared to those from constant pressure decline tests. Based on the experimental results, a mechanistic model for solution gas drive in heavy oil was proposed to explain the linear relationship between the oil production and depletion pressure.