The principal flame cutting fuels are acetylene, methylacetylene-propadiene (MPS), natural gas, propane and Praxair's FG-2^TM gas.

Acetylene (C₂H₂)
Acetylene has a high heat release in the primary flame and a low heat in the secondary flame. It has the hottest flame temperature of the commercially available fuel gases (6,300°F) and is an excellent choice for welding, brazing and cutting of steel alloys less than 2 inches in thickness.

Methylacetylene-propadiene (CH₃C:CH)
Methylacetylene-propadiene-stabilized fuel gas has a high heat release in its primary and secondary flames. The heat release in the primary cone is slightly lower than acetylene. The outer flame temperature is similar to propane and FG-2 gas.

Methylacetylene-propadiene-stabilized mixtures combine the qualities of an acetylene flame with a more even heat distribution. The mixture burns hotter than propane or natural gas.

Methylacetylene-propadiene-stabilized preheat flame (inner cones) are at least 1.5 times longer than acetylene preheat flame (inner cones) when used with one-piece tips. Gases of this type commonly use two-piece tips, which will help to lessen preheat times and have the same length cones as acetylene. Training is often required in order to use methylacetylene-propadiene-stabilized fuel gas to its best advantage.

Natural gas (Methane CH₄)
This product is usually supplied through low-pressure pipelines from a local utility. Injector torches are recommended in order to overcome the low delivery pressure. Preheat time is longer than the other commonly available fuel gases. One benefit is that cylinders and bulk storage vessels are not required.

The cost of natural gas is less than other fuel gases, but increased preheat times usually make this a false economy.

Propane (C₃H₈)
The flame temperature of the oxy-propane flame is lower than acetylene and Praxair's FG-2 gas flames. The primary flame releases low Btu when compared to the FG-2 gas or acetylene, which increases preheat time. The heat distribution in the flame can be an advantage with thick material.

Propane is commonly used by scrap yards where cut quality is not critical. Where cut quality is not a concern, propane may be a cost-effective fuel gas.

Praxair's FG-2 Gas
The FG-2 gas from Praxair has high heat release in its primary and secondary flames. The heat release in the primary flame cone is similar to acetylene. The BTU capacity of the outer flame is superior to that of acetylene. Praxair's FG-2 gas combines the qualities of an acetylene flame with the secondary heating capacity of the propane. The fuel gas burns hotter than propane; however, the cutting speed should be calculated on a case by case basis before choosing this as the most economical choice as your fuel gas.

It offers superior cylinder pressures with excellent withdrawal capacity at low services temperatures. With many applications it is not necessary to manifold FG-2 gas cylinders together in order to give the required gas flow rate. It is a chemically pure gas that is not a mixture.

Praxair's FG-2 gas preheat flame cones are at least 1.5 times longer than acetylene preheat cones. Training is often required in order to use the FG-2 gas to its best advantage. A two piece tip is usually recommended.