Oily Biome

The Oily Biome is a hot subsurface biome built around crude oil and the structures that support its extraction. It usually sits directly above the Volcanic Biome, though world generation can place it elsewhere if the asteroid has the Irregular Oil trait. Its temperature ranges from roughly 80 °C at the top to 380 °C at the bottom, making it one of the most hazardous regions to explore without heat protection.

In its normal form, the biome contains Crude Oil, Oil Reservoirs, veins of Diamond, Granite, Lead, and Iron Ore, plus pockets of Natural Gas and Carbon Dioxide. Slicksters inhabit it, and the terrain can also include small vacuum pockets. Very small amounts of Petroleum may appear if the temperature is high enough to convert Crude Oil, and in some worlds the bottom can naturally contain Petroleum and Sour Gas due to extreme heat. Crude oil is often under pressure, which can eventually rupture thin natural tile borders between pockets.

Several terrain features can appear here, depending on the biome variant:

• Oil Well: a Crude Oil lake with an Oil Reservoir, surrounded by Carbon Dioxide, Igneous Rock, and Granite.
• Small Diamond Deposit: a smaller version of the Diamond Deposit feature.
• Diamond Deposit: a larger Diamond deposit, usually surrounded by Iron Ore and Igneous Rock.
• Frozen Crude Oil Pond: in Frozen variants, Crude Oil is converted into Solid Crude Oil and appears as a frozen deposit surrounded by Igneous Rock, Granite, and Lead.
• Dry variant: does not contain Crude Oil, but still includes a Small Diamond Deposit feature.
• Patch variant: contains less Crude Oil than the base version and includes an Oil Well feature.
• Patch Double variant: similar to Patch, but with two Oil Well features.

The Oily Biome is a major late-game resource zone because Oil Reservoirs provide a renewable source of crude oil, which can then be refined into useful fuels and materials. Exploration is worthwhile despite the danger, and Atmo Suits are strongly recommended to deal with both the heat and the biome’s hostile conditions.