Why do oil rigs have those fires on top?

I've always wondered why oil rig things have those fires on top. Does it serve some purpose or is that just what happens when they strike oil?Why do oil rigs have those fires on top?
In all such installations i.e. oil rigs,refineries etc dealing with flammable natural gases[CH4,C3H8,C4H10 etc],there are chances that mixture of these with air may produce explosion on exposure to a ignition source.To mitigate the risk of explosion the mixture of them in limited quantity %26amp; in controlled condition kept to burn regularly , as a burning mixture can not explode.Why do oil rigs have those fires on top?
the oil refining process has many byproducts, many of them aren麓t of any use. The combustion of an organic component results in carbon dioxide plus water, which are far healthier for the enviroment than the oil gases... so fire them up baby!!
It burns natural gas that is also mixed in with crude oil in deposits. If they didn't burn it, it could fill up the area around the drilling deck and explode.
Im pretty sure it is there to burn the natural gas it gathers when getting oil.