Petrol price rising fast, and likely to keep going On the rise: The spike in petrol prices is in line with a lift in the average national petrol prices over the past two months. Australian petrol prices have recorded their fastest jump in four years and will likely continue rising. From the low-point in the price cycle in mid-May of $1.30 a litre, the average price at the Sydney pump has hit $1.55. For a 60-litre family car filled up once a week, that amounts to an increase of nearly $800 a year to the fuel bill. The spike is in line with a lift in average national petrol prices over the past two months, the steepest for nearly four years, according to analysis by Commsec. Of course, prices fluctuate on a daily basis: last week, Sydney's average fuel price was cheaper than anywhere but Melbourne at $1.48 but by late Monday, it had risen to $1.56. "The sustained high global fuel price and a weaker Australian dollar are having a double whammy effect for motorists," CommSec's Savanth Sebastian said. The bad news is prices are only likely to go higher. Wholesale fuel prices are inching higher and CommSec predicts the price at the pump will rise by as much as 3¢ over the next fortnight. Geoff Trotter from Fueltrac said the distorting power of supermarket discount dockets was pushing prices higher. Mr Trotter said the retail price of fuel in Brisbane had hit $1.66 a litre on the weekend, despite the city's wholesale prices being comparable to Sydney. Mr Trotter blamed the increasing generosity of Coles and Woolworths fuel docket discounts, which have reached as high as 45¢ a litre on shoppers meeting stipulated spending conditions.