This paper provides an empirical analysis of the impact of various influences on carbon dioxide emissions. It incorporates methodological refinements of input-output structural decomposition analysis, which is the examination of economic change by means of a set of comparative static variations in key parameters of I-O tables. The analysis is performed using a two-tiered KLEM model, which allows for estimation of substitution and technological change effects within and between input aggregates. The model is used to decompose the sources of change in CO2 emissions in the U.S. over the 1972–82 timeframe using hybrid energy/value tables for the initial and terminal years. Results show the significant effect of substitution within the energy sector and between energy and other inputs as the leading causes of the decline in carbon dioxide emissions.