Sheffield, Pioneer's founder and a high-profile figure in the shale industry, has been barred from joining Exxon's board, according to the agreement reached between the companies and the FTC.
Demand for the heavy-machinery fuel that powers everything from commercial trucking fleets to construction equipment is weakening in many of the world's largest economies.
Further data obtained by scene investigation has strengthened leads pointing to a Chinese-owned vessel as the cause behind the leakage of a gas pipeline between Estonia and Finland.