Orthocarbonic acid, carbon hydroxide, methanetetrol is the name given to a hypothetical compound with the chemical formula H4CO4 or C(OH)4.

Its molecular structure consists of a single carbon atom bonded to four hydroxyl groups.

In theory it could lose four protons to give the hypothetical oxocarbon anion orthocarbonate CO4−4, and is therefore considered an oxoacid of carbon.

Researchers predict that orthocarbonic acid is stable at high pressure; hence it may form in the interior of the ice giant planets Uranus and Neptune, where water and methane are common.

[10] Polyorthocarbonates are stable polymers that might have applications in absorbing organic solvents in waste treatment processes,[11] or in dental restorative materials.