The apparent viscosities of Nigerian oil sand bitumen were measured over a temperature range of 50-110 degrees C and a shear rate range of 60-320 s(-1). Apart from temperature which is the most important variable influencing the viscosity of a liquid, the viscosities of the bitumen are affected by shearing effects. The apparent viscosity of the bitumen depended on the rate of shear at which it is measured, that is, it has an unlimited number of apparent viscosity values as the shear rate was varied. The shearing effects decreased as the temperature increased; that is, the bitumen became more Newtonian in the higher temperature region.