A theoretical framework combining the two branches of TCE, i.e., the governance branch (Williamson, 2005) and the measurement branch (Barzel, 2005) may explain the choice of the governance structure for private environmental transactions. Four case studies, i.e., the market for pure air in polluted cities, the contractual arrangement between La Esperanza and the Monteverde Conservation League, the case of the French mineral water bottler Vittel and the case of landownership by land trusts are briefly developed in order to support the theoretical framework. Special attention is devoted to the presence (or not) of a 3-D (defined, defended and divestible) property rights system and its influence on the way environmental property rights are likely (or not) to be re-arranged. Lessons and policy implications are drawn in order to foster research on these challenging issues.