The Automobile Association predicts the retail price of LPG will plummet like petrol - but it won't happen overnight.
The price of 91 octane is now at $1.48.9 per litre and the association expects it to fall much further.
However, LPG is $1.34.3 per litre, 13 cents more expensive than diesel (currently $1.20.9 per litre).
The association says LPG needs to be at least 40c cheaper than petrol to be economical and the reason it has not yet dropped is because of a "locked" pricing structure.
