This study attempts to estimate environmental efficiency and production efficiency using a cost function model considering undesirable outputs and then compares environmental intensity efficiency (EIE) determined using these two efficiencies with conventional environmental intensity. The EIE was estimated using the simultaneous model of production efficiency and environmental efficiency based on Stochastic Frontier Analysis (SFA) and then compared against the environmental intensity determined in the traditional way. Considering the estimation of CO2 emissions, labor, fossil energy, and output are positively and significantly related to CO2 emissions at the 1% level. Fossil fuels have an estimated coefficient of 0.795, indicating a more significant impact on greenhouse gases than other variables. The CO2 emissions are not particularly efficient, but they are increasing by about 0.5 percent per year. The most environmentally efficient countries are, in order, high-, low-, and lower-middle-income countries. There is also an increasing trend in production efficiency yearly, with the highest being in the high-income and OECD (Organisation for Economic Co-operation and Development) groups, respectively. The EIE, calculated from production and environmental efficiency, is also rising. EIE values are highest in high-income countries due to their higher production efficiency and environmental efficiency. Conversely, OECD countries have the lowest EIE as a result of their high production efficiency combined with low environmental efficiency. Our EIE results differ significantly from