This is also an interesting and well-known report discussing the non-mechanical response to the Valdez spill from 2006: http://www.pwsrcac.org/wp-content/uploads/filebase/programs/...
I can't be clear enough on this -- the impact of dispersants on the environment and their lack of efficacy at actually decomposing oil (see: resurfacing) was well-known at the time of the Deepwater Horizon spill. There's ample discussion from the actual professionals in this field at the time of the incident regarding the obviously inadequate cleanup process. The responses from both BP and the EPA were meant to reduce metrics like visible sheen while ignoring the environment (it's even worse in the gulf since current variation at depth results in a much broader resurfacing pattern than simply leaving the oil on the surface would have done).