This paper examined the factors that determine the carbon dioxide emission in USA, Japan, China and India during the period 1970 to 2008. The statistical results show that increased CO_2 emission is a factor of increased fuel consumption across countries, and does not happen simply due to the passage of time. The results of the panel, indicate a direct relation with fossil fuel consumption but not as much with the population increase. There is minor variation in the results of fossil fuel consumption variables across countries, in case of coefficients being statistically significant. However, the significance level is very low in case of population variable in some of these countries. The panel data analysis suggests that the carbon dioxide emission is mainly a factor of heavy fossil fuel consumption, and not merely due to increase in population.