This photo shows three Johnson Matthey emissions control systems installed on top of three caterpillar diesel engines on a Shell drill rig in the Pinedale Anticline. These devices eliminate 90-95% NOx emissions from the diesel drill rig engines. Shell has installed these devices on all their drill rigs. Diesel engines outfitted with these devices emit less NOx than natural gas drill rig engines, said Jim Sewell, Environmental Engineer for Shell. Photo courtesy Johnson Matthey.