Cross-country assessment of carbon dioxide (CO₂) emission performance provides quantitative information for determining the responsibility of various countries in reducing global CO₂ emissions. This paper proposes a nonparametric metafrontier approach to evaluating the CO₂ emission performance of 49 major emitting countries. It has been found that the CO₂ emission performance of different countries shows a large discrepancy and the performance level of the group frontier is higher than that of the metafrontier. These countries can be divided into three categories based on their performance levels of group frontier and metafrontier. American’s CO₂ emission performance is closest to the best practice of world countries. Although Asia is still further from the efficient frontier and its CO₂ reduction potential is the highest, the gap has narrowed over time. The technology gap of the sample countries in CO₂ emission performance has experienced two stages of decrease and increase.