By-product of oil refining

Usage examples of ethane.

Under the uniform orange glow which suffused everything, the lake's liquid ethane sat like a basinful of crude oil, thirty miles across.

The air seemed a little clearer here, in the middle of the lake, perhaps because of the constant dissolving and exsolving of gases from the ethane.

One plausible current conjecture is that Titan has an ocean—but an ocean of ethane and methane, rather like liquefied natural gas.