Diesel prices dropped eight cents in January and are currently $1.50 per litre.
The Automobile Association says the price was driven down by the exchange rate climbing to 82 cents against the US dollar in January - a rise of four cents.
The AA says the rising exchange rate makes it cheaper to import fuel, so both diesel and petrol prices should be coming down.
The retail price of 91 octane petrol is $2.11.9 per litre and 95 octane is $2.19.9 per litre.
