FuelWatch encourginging Perth drivers to fill up tonight as petrol prices will rise tomorrow Motorists have been warned the average price of unleaded petrol in Perth is set to rise 8c a litre tomorrow. FUELWATCH is advising Perth drivers to fill up today to save money. The average cost of unleaded petrol is set to increase by about 8c a litre tomorrow to $1.42/L. Tomorrow most BP sites are increasing their unleaded prices by 16c/L to $1.50/L. The majority of Coles Express sites by 12c/L to $1.45/L, most Puma Energy sites up to $1.43/L and the majority of Gull, Caltex and Caltex Woolworths sites up to $1.42/L. Meanwhile Peak sites will be around $1.41/L. Perth's weekly petrol prices, on average, are cheapest on Tuesday and Wednesday and at their most expensive on Thursday and Friday. Originally published as Fill up today to avoid price pain tomorrow