[Jango]

I changed my mind Chlorine can't kill you so fast. (But maybe, it the pressure is VERY high, as Oddworld is very big, chlorine may kill instantly)

Chlorine can kill instantly in very high concentrations, as you see in Oddworld. The chlorine concentration on the screen (if the gas is chlorine) is very high, due to the deep, green colour.

But I guess there is a possibility that it could be Oddinium. There's no evidence against the Glukkons developing it, however there is no evidence in any of the Oddworld games that Glukkons do make a gas called Oddinium. Also, the 'ium' in the word suggests that it is some sort of metal alloy, not a gas (e.g: platinum, magnesium, titanium etc).