This paper reports on an in-depth analysis of the U.S. cement industry, identifying cost-effective energy efficiency measures and potentials. We assess this industry at the aggregate level  (Standard Industrial Classification 324), which includes establishments engaged in manufacturing  hydraulic cements, including portland, natural, masonry, and pozzolana when reviewing industry  trends and when making international comparisons. Coal and coke are currently the primary fuels  for the sector, supplanting the dominance of natural gas in the 1970s. Between 1970 and 1997,  primary physical energy intensity for cement production (SIC 324) dropped 30%, from 7.9 GJ/t to  5.6 GJ/t, while carbon dioxide intensity due to fuel consumption (carbon dioxide emissions  expressed in tonnes of carbon per tonne cement) dropped 25%, from 0.16 tC/tonne to 0.12  tC/tonne. Carbon dioxide intensity due to fuel consumption and clinker calcination dropped 17%,  from 0.29 tC/tonne to 0.24 tC/tonne. We examined 30 energy efficient technologies and measures  and estimated energy savings, carbon dioxide savings, investment costs, and operation and  maintenance costs for each of the measures. We constructed an energy conservation supply curve  for U.S. cement industry which found a total cost-effective reduction of 0.6 GJ/tonne of cement,  consisting of measures having a simple payback period of 3 years or less. This is equivalent to  potential energy savings of 11% of 1994 energy use for cement making and a savings of 5% of  total 1994 carbon dioxide emissions by the U.S. cement industry. Assuming the increased  production of blended cement in the U.S., as is common in many parts of the world, the technical  potential for energy efficiency improvement would not change considerably. However, the cost effective  potential, would increase to 1.1 GJ/tonne cement or 18% of total energy use, and carbon  dioxide emissions would be reduced by 16% (due to the reduced clinker production). This  demonstrates that blended cement production could be key to a cost-effective strategy for energy  efficiency improvement and carbon dioxide emission reductions in the U.S. cement industry.