The use of greenhouse gas emission rights as financial collateral and the feasibility of their enforcement by sale or appropriation raise some issues, such as discerning the legal nature of emission rights under securities law, their suitability for the creation of limited rights and liens thereupon, or the requirements applicable to the perfection, validity, enforceability or admissibility of such collateral so that they can be invoked against third parties - which in turn determine the practical value of such guarantees as credit protection instruments. In this article we aim to address these issues under the current Spanish system and to project it into the future, for the period 2013-2020, when major changes in the EU scheme for greenhouse gas emission rights will come into force.