Major Australian supermarkets have given consumers some form of relief when bread and milk products sitting on their shelves saw significant reduction on prices but the initiatives appear to have been cancelled out by soaring petrol cost currently in effect.

According to FUELtrac, a fuel monitoring body, present fuel prices offered by Cole and Woolworths petrol outlets effectively offset the benefits gained by consumers on falling bread and milk costs.

FUELtrac general manager Geoff Trotter said on Monday that petrol prices moved up by 19 cents per litre to more than $1.40 during the weekends, which he alleged is a coordinated decision by Shell Coles, as reflected on pump prices offered by the firm's service stations in Brisbane, the Gold Coast and the Sunshine Coast.

Trotter told AAP that Shell surprisingly hiked its prices when wholesale costs are plunging as he noted that "the effective Shell wholesale price was 124.37, which meant they were making a retail margin of over 19 cent a litre."

Petrol prices last breached the $1.40 mark was in the second half of 2008, at a time when global fuel prices averaged $US148 and the Australian currency was valued at about 98 cents, according to FUELtrac.

Trotter attributed the high cost of petrol to the dominance currently enjoyed by giant supermarket players in retailing petrol products, which he said allowed them to manipulate fuel prices prevailing in the market.

He argued that major retailers have been controlling a sizeable chunk of the groceries market and more than half of the retail petrol market, which is a scenario that points to inevitable link on these companies' groceries and petrol operations.

Trotter said that Coles and Woolworths are currently waging a price war in bread and milk and whatever cost that they had to sacrifice to edge out one another, "fuel is a wonderful way to recover that margin if there is an opportunity for them to cross subsidise."

Also, FUELtrac pointed to the fact "there was nothing happening in the Australian wholesale price or international prices to explain that jump across those all markets to that level."