Motorists in Australia's two biggest cities can expect the good times at the bowser to sweeten even further as the global oil price plunged to a six-year low, while rural centres continue to miss out on the benefits.

Petrol prices in Sydney and Melbourne have dropped by over 40c per litre since July, as prices of unleaded petrol on Tuesday hit an average of $1.09 in Sydney and $1.10 in Melbourne.

Plummeting: The price of fuel in Sydney continues to fall. Pictured is a Tempe petrol station on January 6, 2015. Credit:Dominic Lorrimer

Sydney motorists filling up with E10 have enjoyed below-dollar prices for over a week, with some stations in southern Sydney going as low as 97.5 cents.