The Sludge Fen is an oil field found on the northeast corner of the Northern Barrens. Occupied by the Venture Company for their oil refining projects, the fen is one of the oil platforms that can be visited in-game. This is a dangerous area to adventure in, as the cowardly Venture Co. employees will rush for help if they are attacked. Sludge Fen is led by Tinkerer Sniggles, Foreman Grills and Engineer Whirleygig.(or the Sludge Fens)
During the Legion Invasions, the area was taken over by Oilrig Bombers, Oilrig Snipers and Oil Rig Engineers. Whether the goblins belonged to the Venture Company, Steamwheedle Cartel or the Bilgewater Cartel is not clear. However, the bombs located there can also be found in Gadgetzan, implying that the goblins were from the Steamwheedle Cartel, likely from Ratchet.
In the RPG
The Sludge Fields is found in the Barrens' northern hills and the Venture Company has an operation there. They have built a derrick over what appears to be a large tar pit, and the operation is led by a goblin known as Supervisor Lugwizzle.