Methane tanks are back mounted, moderately large, and resemble small fuel tanks of modern trucks. When they are of the large variety, they provide a place for the creatures to breathe their methane atmosphere outside of their suits. Thus, Unggoy remove their suits when entering the huge methane filled tank, as they are not needed. On the battlefield, Unggoy use portable methane recharge stations to refill their methane supplies.
The tanks of Heretic Unggoy look quite different from their Loyalist counterparts. Instead of being pyramid, or curved pyramid-shaped, they are two tube-shaped ones, with visible smaller tubes that connect it to their mouthpiece in which they breath the methane from.
The Covenant allow Unggoy to use various types of methane chambers when they are not in battle. There is a main chamber for the Unggoy to reside in and a smaller chamber in front where the Unggoy can change into and out of their suits. These structures often have posted guards to prevent the creatures inside from being caught off guard, and airlocks on their entrances. A number of different types of methane chamber exist, the atmosphere pit, which is a more temporary, ground-based version, and the methane suite, a ship-board variant.
- When shot in Halo Wars, Halo: Reach and Halo 5: Guardians, the tanks sometimes explode due to methane's high flammability.
- It is noted in the Halo 3 level Sierra 117 that the Jiralhanae may have added some form of addictive gas, possibly a type of infusion, that increases the Unggoys' bravery and willingness to fight. This is supported by the Final Grunt's words ("...it's the gas. When I'm on the gas, I don't know what I'm doing half the time!"). However, as the Final Grunt was meant as an easter egg, this cannot be confirmed. It is also possible that being under the Jiralhanae's leadership, who threaten to slaughter the Unggoy for meat, is responsible for their increased bravery, as suggested by Thel 'Vadam.
- The color of the methane released from the tanks changes between the games. In Halo 2, Halo 3, Halo Wars and Halo 3: ODST, the methane is blue. However, in Halo: Reach and “Halo 5”, it appears green. The gas is not seen in Halo: Combat Evolved, as the gas tanks cannot be removed nor are there any transparent tanks like the heretic variant. It should also be noted that in real life, methane is colorless.
An Unggoy Ultra with its methane tank.
A different variant of the methane tank, used by a Special Operations Unggoy.
An Unggoy with the methane tanks used in Jul 'Mdama's Covenant faction.