This paper provides an empirical study of optimal carbon tares and welfare effects under incomplete international climate agreements when there are market failures in the cooperating countries. The objective of the group of countries taking part in the international climate agreement is to design carbon tares that maximize their aggregate net income, subject to a constraint on global CO2 emissions. We use a numerical energy model to study scenarios that differ with respect to types of CO2 taxes and countries taking part in the climate agreement. We also discuss the impact on regional net income following from different international climate agreements.