JUNE 1999 · VOLUME 20· NUMBER 6

To obtain the figures for companies' contribution to carbon emissions, for each company, 1997 production data for coal, petroleum, and natural gas were obtained from company data disclosed to the Securities and Exchange Commission (SEC) and from industry trade journals. Daily production numbers were converted to annual production.

Where producing companies identified the nations where their oil, natural gas, and coal were produced, production was converted from physical units to British thermal units (Btu) using Energy Information Administration Gross Heat Content factors for production of fossil fuels by country. In cases where the location of production was not identified, average regional factors were used.

The carbon content was calculated by multiplying energy production by the specific carbon coefficients for each fuel in millions of metric tons of carbon per quadrillion Btu (Quads): 25.74 for coal; 20.25 for oil; and 14.47 for natural gas.