Oil sand hydrotransport technology has become increasingly important to Syncrude Canada Ltd. and the oil sands industry. Oil sand slurries are complex, multiphase mixtures of bitumen, coarse solids, fine solids, water and air that can exhibit time-dependent behaviour, wherein pipeline friction losses increase drastically with time. Four separate experimental programs were conducted to study the effect of bitumen on pipeline hydraulics using 100 mm and 250 mm (I.D.) recirculating and once-through pipeline loops. The results show that pipeline friction losses increase as a bitumen coating forms on the pipe wall. The effect is more pronounced at 50 degrees C, but also occurs at lower temperatures.