What is the efficiency of refining petroleum?

Your question is about the "process energy balance" of refining crude oil. If you meant to include the amount of energy expended in exploration and recovery the problem becomes much more complicated and many more variables are introduced. The datapoint I can give you is 4.98:1 for diesel fuel refined from petroleum. In comparison to your "refining efficiency" example for hydrogen, that 70-80% value would be expressed as 0.7:1, or the diesel ratio expressed as a percentage would be 498%, compared to 70% commonly given a the maximum efficiency for producing hydrogen from electrolysis (80-95% is the theoretical maximum efficiency and in reality commercial hydrogen processes today only achieve about 0.3:1 or 30%.) For each unit of energy that goes into the processing of crude oil, 4.98 units are available in the fuel product. This is from: Sheehan, J., Camobreco, V., Duffield, J., Graboski, M., & Shapouri, H. (1998). An overview of biodiesel and petroleum diesel life cycles. National Renewable Energy Laboratory. Golden, Colorado. http://www.nrel.gov/docs/legosti/fy98/24772.pdf For the process energy balance it is still wise to consider that all crude oil does not have the same energy content, nor does it have consistent chemical composition. Crude oil varies widely in molecular composition which is somewhat related to the viscosity rating for crude, known as the API rating. Crude oil used today varies from about 12 API, which is very heavy tar-like crude, to high 40's, which has lighter shorter hydrocarbon chains and contains much more volatile components. Contaminants in crude such as sulphur may require more energy to remove, depending on local regulations or process requirements, so the ratio will even vary according to the purity required. Since different refineries are built specifically to use different grades of crude oil, and produce various hydrocarbon products, the actual process energy balance is quite hard to determine for a general number. Today processes such as those that can convert natural gas to diesel fuel, making ultra-clean diesel, may change the numbers even more. Other petroleum-sourced fuels such as condensate contain propane and butane in essentially pure forms and require almost no processing so they likely have much higher ratios than that given for diesel fuel. Also see this reference which contains a useful bibliography related to both fossil energy ratios and process energy ratios: http://biofuels.coop/education/energy-balance/ For hydrogen efficiency information see the powerpoints listed on this website: http://www.bren.ucsb.edu/academics/course.asp?number=288