The Unggoy's homeworld, Balaho, has a Methane-rich atmosphere and as such Unggoy breathe methane gas. Thus, when they are in a Oxygen-rich atmosphere, like that of the Halo installations or Earth, they need to wear a methane gas tank. When Unggoy are in battle, they may run low on their supply of methane, so they must have a ready supply nearby if required. These tanks contain the ready supply of Methane Gas the Unggoy need.
They are short and round in shape, purple in color and have a large blue valve on the top. The Methane Tanks are seen generally where Unggoy are operating. The tanks are also highly explosive due to their methane content.
- If the blue "X" on the tank is shot at it will ignite and burn for a while before exploding.
- Battlefield Methane Tanks appear in Halo 2 and Halo: Reach. In gameplay terms, they are similar in function to Plasma batteries in Halo 3, as they both explode when shot at.
- They seem to resemble Gravity Thrones that the High Prophet Hierarchs use.
- A new version of the Battlefield methane tank appears in Halo Reach. It is highly explosive and will start to leak gas when it is about to explode. They can hold four Unggoy.