The 'big four' supermarkets should be blamed for the high fuel prices, claims the RAC.
The average price of petrol fell by 6p-a-lire in November, but according to the RAC, it should be over twice as much.
With the wholesale price of petrol and diesel falling, the overall sale price should be 14p-15p lower than it currently is.
The RAC has claimed that Asda, Morrisons, Sainsbury's, and Tesco's failure to cut fuel costs have left the companies with a profit margin of 20p for every litre sold.
Unleaded fell from 165.96p at the start of November to end the month at 159.88p, whereas diesel dropped from 190.31p to 183.87p, saving motorists more than £3 a tank, but the RAC believes it should have been more.
Wholesale petrol dropped by 11p from 122.63p to 111.53p and diesel decreased more, coming down 15p from 143p to 128p.
Taking an average of wholesale prices for the last week of November, the RAC believes petrol should be at an average of 146p and diesel 169p – 14p and 15p lower than the current averages.
RAC fuel spokesman Simon Williams said: "It's bordering on a scandal that drivers are being overcharged so much because the big four supermarkets, which dominate UK fuel retailing, are flatly refusing to reduce their prices by bigger amounts.
"Their prices are dropping like a feather when they should be falling like a stone.
"In 10 years of closely monitoring fuel prices, we have never seen major retailer margins this high for this long.
"This sadly seems to be a thing of the past as nowadays they appear to be hanging on to massive margins for dear life,"
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