With regard to major spills, the coast guard would work with all available partners to respond. The system remains a polluter pay and a polluter responsibility, so the shipowner would be primarily responsible and then the response organizations would be involved. If the shipowner were unable or unwilling to respond, then the coast guard would take over as the primary responder to the incident. It is very much a system of cascading resources to respond in the best possible way as a total partnership. No one agency can respond on its own.
If I go back to the question asked earlier regarding a spill the size of Deepwater Horizon, 16 countries supported the U.S. government, the national guard. It wasn't the U.S. coast guard on its own or any single federal agency; it was a multiplicity of support and response.