Experimental simulations of model well-bore flows in laboratory pipelines show that frictional energy losses (i.e., pressure drops) are reduced when water is present with heavy oil. The reduction has been shown to increase with the water fraction. The mixtures are not oil in water emulsions in the classical sense of the term. At the low axial velocities which characterize wellbore flows, the flow regime is inherently intermittent. Using a variety of methods the structure of the flow has been examined to identify the flow regime and the cause of the reduced pressure gradients. It has been found that the water travels as large slugs and that oil is invariably present at the wall when the mixture flows through a steel pipe. The evidence suggests that a significant fraction of the oil is transported within the water slugs. A tentative flow regime boundary between the regions of intermittent and continuous water-assisted flow is proposed in terms of the mixture Froude number and the injected water fraction.