Since the implementation of the Environemental User Fee System (EUFS) in the Laguna de Bay Region in 1997, there has been no comprehensive evaluation of its impacts particularly at the regulated firm level. This study, therefore, is an attempt to generate empirical evidence that could explain the differential behavior of regulated firms toward the EUFS. The emphasis of analysis is at the firm level, since firms are crucial stakeholders whose cooperation spells the difference between pollution or non-pollution, or between acceptable levels of pollution and excessive levels. The sources of information for this study include: a) a survey of 89 firms regularly monitored by the Laguna Lake Development Auhtority (LLDA) from 1999-2004; b) 170 firms with self-monitoring reports (SMRs) for 2002 and environmental performance indicators for 1999-2004; and c) dissemination seminars for firms and the regulator. Using a conceptual framework modified from Doonan, et al. (2002), environmental performance is modeled (using the EQS 6.1 Build 88) as a series of events wherein different sources of pressure induce firms to undertake activities and actions which subsequently affect the firms' environmental performance. Compliance rate (%) to the standard of 50 mg/li Biological Oxygen Demand (BOD) was used as a measure of ernvironmental performance.