Motorists are being encouraged to fill their tanks before the price of petrol gets a double hit from GST and a higher excise on 1 October.
The Goods and Services Tax will rise on Friday from 12.5% to 15% and a fuel tax on petrol will also rise.
The Automobile Association says the excise on petrol will equate to an extra 3 cents per litre and GST an additional 4c.
It says motorists are used to petrol increases, but 7c is more than usual.
Diesel will increase by 3c a litre.