Whiteway Motors and Pulse Fuels in Braye Road were the cheapest in island until last week, but their prices have risen sharply.
Whiteway Motors has seen an 18p per litre increase on unleaded fuel, from 161ppl to 179ppl.
Owner Andre Whiteway said: ‘We try to be as competitive as we can, but there’s only so much we can do.
‘I try to keep my prices down in the interests of the general public.
‘I look at it that if I can do more volume, I can still make a living.’
Both Whiteway Motors and Pulse Fuels are supplied by the Guernsey Petroleum Distributors.
Mr Whiteway said fuel shipments from GPD come in about every five weeks, and the prices can change with each shipment.
He added that he expects Whiteway to be top of the table again in the near future.
‘My prices wont alter until the next boat comes in,’ he said.
Mr Whiteway added that since putting up his prices, he had seen some customers view the price sign and drive off.
Pulse Fuels upped its unleaded prices from 162ppl to 181ppl last week, a 19ppl increase.
Manager Elliot Gallienne said: ‘The most important thing to us is our customers.
‘While it might seem like a huge price increase, other places may increase their prices every few days, but our price will be the same for the next four or five weeks.'
Mr Gallienne added that it was the company's policy to keep the same margins no matter how much the supplier charges.
‘We have no say what the prices will be. With how volatile the market is at the moment, it is difficult to say what will happen.’
The Channel Islands Coop saw a 2ppl increase yesterday on unleaded fuel, from 180.9ppl to 182.9ppl.
All Rubis outlets are also likely to see a price hike as suppliers increase their unleaded motor spirit by 4ppl.
As of 17 June, the cheapest place on island for petrol was St Martin’s Garage, at 174.9ppl for unleaded fuel and 178.9ppl for diesel.