This paper presents a model of imperfect international competition. Within this framework, the optimal choice of national environmental policy instrument and international emissions trading scheme is discussed. The choice of national instrument is restricted to absolute and relative standards, which form the basis for permit and credit trading respectively. It is shown that relatives standards and credit trading lead to higher output than emission ceilings and permit trading. I find that governments want to increase production beyond the level reached with emission ceilings and therefore prefer relative standards. Furthermore, international emissions trading is only optimal when the country imports emission quotas, and in several cases, governments will choose not to allow international emissions trading.