Production of iron and steel is an energy-intensive manufacturing process. The energy efficiency of steel production has a direct impact on overall energy consumption and related carbon dioxide (CO2) emissions. The goal of this study was to develop a methodology for accurately comparing the energy-related CO2 emissions intensity of steel production in different countries and to demonstrate the application of this methodology in an analysis of the steel industry in China, Germany, Mexico, and the U.S. Emissions intensity values are often sought by policy makers who must decide questions related to energy, greenhouse gases, and competitiveness. Our methodology addresses the industry's boundary definition, conversion factors, and industry structure. The results of our analysis show that, for the entire iron and steel production process, the base-case (2010) CO2 emissions intensity was 2,148 kilogram (kg) CO2/tonne crude steel in China, 1,708 kg CO2/tonne crude steel in Germany, 1,080 kg CO2/tonne crude steel in Mexico, and 1,736 kg CO2/tonne crude steel in the U.S. One of the main reasons that Mexico has the lowest CO2 emissions intensity is Mexico's large share of steel production using electric arc furnaces (EAFs) (69.4%). EAF steel production has lower CO2 emissions intensity than production using blast furnaces/basic oxygen furnaces. China, by contrast, has the smallest share of EAF production among the four countries – 9.8% in the base-case year 2010. In one scenario, we applied the Chinese share of EAF production to the other three case-study countries; the result was an increase in CO2 emissions intensity of steel production of 19% (2,036 kgCO2/tonne crude steel) in Germany, 92% (2,074 kgCO2/tonne crude steel) in Mexico, and 56% (2,703 kgCO2/tonne crude steel) in the U.S. compared to these countries' base-case analyses. In another scenario, we applied the Chinese national average grid electricity CO2 emissions factor from 2010, which is the highest emissions factor among the four countries, to the other three countries. In that scenario, the CO2 emissions intensity of steel production increased by 5% in Germany, 11% in Mexico, and 10% in the U.S. Additional scenarios were analyzed showing that when comparing the CO2 emissions intensities of the steel industry in different countries, it is necessary to take into account the industry structure, especially the share of EAFs and the effect of electricity grid CO2 emissions factors. This report also discusses a number of other important variables affecting steel industry CO2 intensity.