Ethyne, commonly known as acetylene (C\(_2\)H\(_2\)), is the most widely used organic fuel gas in oxy-fuel welding and cutting. Ethyne is the only fuel gas generally suitable for welding steel.

When combined with oxygen, ethyne produces the hottest flame among common fuel gases, reaching temperatures between 3,200 to 3,500 degrees Celsius. This high temperature is necessary to melt steel and other ferrous metals for welding and to rapidly preheat the metal to its kindling temperature for cutting.