Exxon was responsible for the oil spill response that coagulated the oil and sank it. They were surprisingly proud of this, having recommended it to BP so that the extent of leaked oil was less noticeable from the surface.
Exxon also invested heavily in an alternative energy company doing research to create oil from a certain type of algae. The investment was all a PR stunt that gave them enough leverage to shelve the research that was successful enough to be considered a threat.