LPG is a mixture of light hydrocarbons that are gases at normal temperatures and pressures, but liquefy at moderate pressures or reduced temperatures. LPG occurs naturally in crude oil and natural gas production fields and is also produced in the oil refining process.

LPG used as automotive fuel is often referred to as 'autogas'.

The main component gases of LPG are propane (C₃H₈) and butane (C₄H₁₀)

Autogas is a significant transport fuel in light duty vehicles. Beyond petrol and diesel, it has the third largest market share and is estimated to account for at least 8% of all road transport fuel usage by 2010. Australia is currently one of the biggest users of autogas on a per capita basis.

As a key strategy in managing air pollution and greenhouse gas emissions, there is a need for our fuels to facilitate the adoption of future vehicle engine and emission control technologies. There are a variety of fuel properties that could be more tightly managed to bring about improvement in the environmental and vehicle performance of autogas.

The autogas standard, among other things:

• highlights the necessary fuel parameters to improve environmental outcomes and facilitate the uptake of future technologies;
• ensures the quality of autogas in the market place, and possibly assists in the control of residues and other contaminants;
• addresses the possible absorption of excess butane (from the setting of petrol standards) by the autogas market, and;
• complements key government programs which promote the uptake of autogas as an automotive fuel.

Residues contribute to troublesome deposits in regulators and vaporisers, and as a consequence, there are community and industry concerns about the level of residues in autogas. Control of residues is directly managed by the parameter - 'Residue on Evaporation'.

Autogas consists of propane or propane and butane. Residential LPG (used for domestic cooking and heating) consists of propane only.

Fluctuations in the relative levels of propane and butane in autogas is not an unusual phenomenon; it is evident in autogas mixes used in other parts of the world, such as Europe.

Maintaining different mixes of propane and butane is important for the continuation of the autogas market. The fluctuation provides for the flexibility necessary for the distribution of autogas to metropolitan and regional centres.

Certain regional and rural areas are provided with autogas that consists of only propane so that both the domestic and automotive needs can be met with the one tanker load.

The environmental gains from placing constraints on the amount of propane or butane in a mix (ie. 50% butane and 50% propane mix) are not significant enough to limit the autogas market to a set composition.

Some argue that there may even be environmental gains in allowing the level of butane to continue to fluctuate so that the autogas market can operate as a butane 'sink', particularly as there are limited export and domestic petrochemical markets for the use of excess butane.