Using the ISEEM modeling framework, we analyzed the roles of energy efficiency measures, steel commodity and international carbon trading in achieving specific CO2 emission reduction targets in the U.S iron and steel sector from 2010 to 2050. We modeled how steel demand is balanced under three alternative emission reduction scenarios designed to include national energy efficiency measures, commodity trading, and international carbon trading as key instruments to meet a particular emission restriction target in the U.S. iron and steel sector; and how production, process structure, energy supply, and system costs change with those scenarios. The results advance our understanding of long-term impacts of different energy policy options designed to reduce energy consumption and CO2 emissions for U.S. iron and steel sector, and generate insight of policy implications for the sector's environmentally and economically sustainable development. The alternative scenarios associated with 20% emission-reduction target are projected to result in approximately 11-19% annual energy reduction in the medium term (i.e., 2030) and 9-20% annual energy reduction in the long term (i.e., 2050) compared to the Base scenario. (C) 2014 Elsevier Ltd. All rights reserved.