Costco unleaded petrol fell 8p to 147.7p a liter as wholesale prices continued to fall 12p below the average.
Today, diesel prices average 171.6p, almost 14.5p below the UK average. The retailer has 19 service stations across the UK, including stations in Glasgow and Edinburgh.
The drop in prices clearly shows just how high fuel prices are elsewhere. But since Costco is a member-only store, not everyone can get these low gas prices.
Simon Williams, RAC fuel spokesman, said: "Motorists unlucky enough to be a Costo member will no doubt be amazed at how cheap fuel can be sold. It's no surprise to see long queues for gas at Costco. Indeed, recently the queue system at Bristol's forecourt they have had to upgrade to cope with the number of people they want to fill.
"Selling gas and diesel at 12 cents above the average price at the big four supermarkets is concerning. Even though Costco operates on thin margins, the supermarkets have to lower their prices."
“We asked them to cut it by 5p a liter on Tuesday this week, but wholesale prices have fallen since then so they need to cut it by at least 7p.
Earlier this week, motoring experts called on the big four supermarkets - Tesco, Sainsbury's, Asda and Morrisons - to cut fuel prices by 5p "immediately".
Speaking at the event, Mr Williams said: "It's a shame to see the big petrol retailers charging customers an unfair price when they're struggling to make ends meet."
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