The Environmental Defense Centers (EDCs) of Brazil provide response services following oil spill accidents. EDCs near affected areas rapidly organize and execute emergency response activities in order to minimize the environmental and economic impacts of spills. The current research applied ergonomic principles and methods (interviews, direct observation and focus groups) to describe common EDC system operations, and to identify constraints and conflicting procedural practices. Results of ergonomic field studies were modeled and analyzed using the Functional Resonance Analysis Method (FRAM), which can show how functional variability in planning, preparedness, execution, resources, economic and human factors affect the quality of emergency response activities. The FRAM analyses provide guidance for improving the resilience of oil spill emergency response systems. (C) 2016 Elsevier Ltd. All rights reserved.