This report analyses the experience of ten OECD countries in the design and implementation of quantitative indicators used to assess the outcomes of environmental enforcement authorities’ efforts to ensure compliance with pollution prevention and control regulations. To respond to the growing demand for results-oriented work methods and the need for performance management and accountability at the time of severe budget constraints, more and more environmental enforcement authorities are working to develop indicators to characterise improvements in behaviour of the regulated community (intermediate outcomes) or environmental conditions (final outcomes) stemming from their activities. The report considers six types of intermediate and final outcome performance measures, including compliance rates and indicators of improved environmental management practices and reduced risk. Based on the OECD criteria for the evaluation of environmental indicators – measurability, analytical soundness and policy relevance – the paper identifies key challenges for developing and using specific categories of compliance assurance outcome indicators and suggests several ways to improve their effectiveness. The review of a “toolbox” of existing outcome indicators and the analysis of their respective strengths and weaknesses suggests that it is not possible to identify a “best practice” approach or a universal optimal set of indicators. The functionality of individual outcome measures ultimately depends on their purpose (e.g. internal performance assessment or external accountability) and suitability for joint analysis with the enforcement authority’s resource (input) and activity (output) indicators. The report identifies several issues for further analysis.