@mahonj: In the figure, the solid portion of the PHEV results only accounts for GHG emissions associated with gasoline propulsion. Since the hydro scenario only results in GHG emissions from gasoline for the assumed system boundary, the overall GHG emissions for that scenario are equivalent to those from gasoline propulsion. There is an explanation in the figure caption that the left-hand side bars, which only show gasoline related GHG emissions, correspond to the hydro scenario. The vehicle specifications can be found in the supporting information. The difference between the HEV and Prius results can be explained by a more powerful engine and higher curb weight, more aggressive driving cycles, and use of a well-to-wheel system boundary (which includes refining and transport, as you said). @HarveyD: The paper notes that the authors declare no financial conflict of interest.