An update on the study by Ang [Energy Economics 9 (1987) 274-286] shows substantial changes in the relationship between energy consumption and national output across world countries from 1975 to 1997. While the ratio of commercial energy consumption to national output increases across countries as per capita income increases in 1975, the converse is observed in 1997. The cross-country energy elasticity has also dropped from values well above unity to below or close to unity. Using the 1997 data, the relationship between CO2 emissions and national output across countries is studied and the results show some interesting differences from that between energy consumption and national output. (c) 2005 Elsevier Ltd. All rights reserved.