This article assesses private car CO2 emissions and car tax revenue in Ireland over the 10-year period following the introduction of an emissions-based car taxation policy in 2008. This article assesses private car CO2 emissions and car tax revenue in Ireland over the 10-year period following the introduction of an emissions-based car taxation policy in 2008. We build on a model of the Irish car stock, which has new car sales, car fleet mileage, and CO2 emissions intensity data to develop a bottom-up picture of historic CO2 emissions from the car fleet. In this article, we develop a counterfactual scenario following car purchasing trends in EU countries that did not introduce an emissions-based purchase and annual car taxes over the same period.