Oil Ocean Zone

"Robotnik's refineries are pumping at full steam. Crude oil has turned the ocean black! Can Sonic keep his footing on the slippery catwalks and bursting steam vents?"

- Sonic the Hedgehog 2 manual description

Oil Ocean Zone is the seventh Zone in Sonic the Hedgehog 2. As with most other Zones in this game, Oil Ocean consists of two standard Acts with a boss fight at the end of Act 2.

Overview
The underground passageways of Mystic Cave/Hidden Palace apparently lead out to the sea, for Sonic and Tails now find themselves scaling slimy oil refineries off the coast of West Side Island. In a manner typical of the Doctor's environmental ethos, Robotnik clearly isn't too concerned about keeping the maritime habitats of West Side Island in pristine condition (this keeps with his early-on Archie alter-ego who loves to pollute and destroy natural green environments). His drilling platforms have blanketed the ocean in viscous petroleum sludge; the only creatures that move are robotic ones, Octus and Aquis Badniks floating amidst the steel gantries of the rigs.

The oil does, on the other hand, afford Sonic a means of survival should he fall off the level. While the hedgehog can't swim in water, the gloopy hydrocarbons mean you won't sink as long as you keep jumping. Often, floating fans will provide a means to get back to solid ground.

In addition, the Zone hosts strange green/yellow checkered cannons, which throw Sonic back and forth around the level. Flame-propelled gas-burn platforms also provide a means by which to gain altitude (and access secret monitors on occasion).

Boss
In this Zone's boss fight, Robotnik eschews his usual Egg Mobile and attacks via submarine. This oil-faring submersible deploys a variety of weapons, including a spiked harpoon and periscopic laser cannon. It is damaged by attacking the cockpit while it resurfaces.

Sonic the Comic
The Oil Ocean Zone appears twice in the British series Sonic the Comic, and in both cases Sonic was transformed into the psychotic Super Sonic.

In the first instance, Sonic and Tails traveled to the Zone to help their friend Red (who had been called in with his workers to clean up the Zone after the events of Sonic the Hedgehog 2) battle an uncontrollable fire that threatened to spread across the whole Zone. Sonic quenched the fire, but was ambushed by an Aquis Badnik that took advantage of the Zone's layout to drop Sonic in the oil and try to roast him alive. Sonic became Super Sonic, destroying the Aquis before attacking his own friends. Tails managed to calm him down enough to turn back to Sonic, after which Sonic helped Red deactivate all the traps in the Zone.

In the second instance, Sonic and Tails traveled to the Oil Ocean Zone again to deactivate the Pump, a new device designed by Doctor Robotnik to pollute all of Mobius. However, this was all revealed to be a trap by Robotnik to lure Sonic to the Zone so that he could set off a super-bomb that would turn the entire Oil Ocean Zone into a huge fireball. With the detonation in 30 seconds, Sonic sped all across the Zone in search of the bomb, but couldn't find it. Incredibly stressed and with only 14 seconds left, he accidentally ran off a ledge and transformed into Super Sonic. Super Sonic managed to find the bomb and contain it in a cocoon of speed moments before it exploded, saving the Zone and turning back to regular Sonic at the same time.

The Zone is described as being "high in the Northern Hemisphere of Planet Mobius".

Archie Comics
The Oil Ocean Zone appears in issues 217-218 of the Archie's Sonic the Hedgehog comics. It is guarded by a chapter of the Dark Egg Legion and is called the Oil Ocean Refinery﻿ in this continuation. It was blown up and put on fire in Issue 218, and is currently in a state of disrepair.

Trivia

 * The level is also known for a particular bug that causes Sonic's speed to be accelerated and jumping ability to increase, granting him greater speed and jumping ability of Super Sonic or Hyper Sonic (from Sonic the Hedgehog 3 & Knuckles).
 * There is also a neat trick that can be done in which if the player executes a Spin Dash in the oil, they can bypass under some of the platforms, although if the player isn't fast enough, Sonic can sink in the oil and die. This shouldn't be abused in Act 2, however, since the oil just ends at a certain point. In the 2013 re-release, a wall has been added to prevent this and in addition the player is unable to perform the Spin Dash while running on the oil.
 * The wrecking ball from the original Sonic the Hedgehog can be placed in Debug Mode. In the prototype, it is shown that it was a scrapped gameplay mechanic.
 * In the Adventures of Sonic the Hedgehog pilot, a background looks similar to this level.
 * In the original Genesis version of the game, a code could be put in to give the player 14 continues, but this stage's BGM will play throughout the entire game.
 * The official artwork of the Zone depicts the oil being orange, yet in the game it is dark violet.