An experimental study was conducted to investigate the effect of the variable-aperture system of an oil sand fracture on its hydraulic and mechanical response to an increasing confining pressure. The oil sand fracture was induced in core samples along the axis of the sample using the Brazilian tensile test. A computer-assisted tomography (CT) scanning analysis was performed to determine the initial fracture geometry and monitor the closure process. The fracture was shown to be a variable-aperture system, with surface roughness and tortuosity playing an increasing role as the fracture closed under pressure. Flow tests revealed a nonlinear behaviour, deviating from the cubic law, and indicated the roughness effects of a natural oil sand fracture are significant. The mechanical response was similar to that of the hydraulic behaviour, indicating the strong relationship between the two. The nature of the uncemented oil sand was shown to strongly affect the strength of the fracture contacts and, therefore, the general closure process.Key words: oil sand, fracture roughness, fracture aperture, computer-assisted tomograhy, hydraulic conductivity.