The Oil Ocean Zone is a massive valley flooded by the spillage from various oil rigs.
After defeating Dr. Eggman and his assistant, Dr. Julian Snively, at their base on South Island, Sonic the Hedgehog chased the two mad doctors down to Westside Island, where he teamed up with his new sidekick and best buddy Miles "Tails" Prower as well as the Knothole Freedom Fighters. They arrived in Oil Ocean Zone after passing through Mystic Cave Zone in their efforts to defeat the mad doctors, whose goal on Westside Island was major construction and refinements as part of their plan for world domination. From here, they chased them down to Metropolis Zone. (VG: StH2, SSD: #12)