In the past, transportation of heavy and bitumen to downstream refineries has been accomplished by either adding a diluent or converting the vacuum residue to produce a synthetic crude oil. In Canada, partial upgrading of bitumen to enhance its transportation to downstream refineries is becoming more attractive as production increases from both in situ and mining operations. Similar opportunities exist for inland production elsewhere in the world. This review discusses the relationship between the key properties for transport, which are viscosity and density, and the composition of a crude oil. The potential process pathways to achieve low-cost reduction in viscosity and density are discussed, particularly thermal cracking and partial deasphalting. Thermal cracking is effective for reducing the viscosity, but it is limited by the stability of the processed asphaltenes in the product blend. While thermal cracking has a long history in refining, the lower levels of asphaltene removal to achieve partial upgrading require removal of solid asphaltenes, rather than the viscous liquids produced in current refinery deasphalting plants. The benefits of combinations of reaction and separation approaches are discussed, particularly combinations of thermal cracking, addition of reduced amounts of diluent, and partial deasphalting.