Fuel prices in the UK stayed at 145p for petrol and 150p for diesel in July, despite evidence suggesting they could be lower.
This contrasts with Northern Ireland, where petrol costs 140p and diesel 142p on average.
RAC data shows drivers are paying more than necessary, with petrol costing 5p per litre too much and diesel 8p per litre too much.
This translates to almost £3 extra per tank for petrol and over £4 extra for diesel.
Retailer margins for petrol and diesel have increased, standing at 13p and 14.5p per litre respectively, above the long term averages of 8p.
In contrast, supermarket fuel prices were slightly lower, with unleaded averaging 142p and diesel 147p per litre.
RAC head of policy Simon Williams said: “It’s disappointing to see fuel prices remain far higher than they should be, especially after the Competition and Markets Authority (CMA) announced at the end of July that drivers were overcharged by an astonishing £1.6 billion last year.
“With our analysis clearly showing margins are still significantly above the long-term average, it seems like nothing has changed and drivers continue to lose out despite all the ongoing scrutiny from the CMA and the government.”
