Some of the county's supermarkets started charging more than 160.9p per litre of unleaded and 175.9 p for diesel for the first time this week with Sainsbury's and Tesco in Wellingborough topping the list at 166.9p.
That compares to around 150.9 a litre just TWO WEEKS ago.
The RAC says drivers would have to stomach probably more rises this week, but added there is light at the end of the tunnel as oil and wholesale prices appear to be settling down.
Spokesman Simon Williams said: "The latest price hikes are still a result of the oil price rise which began at the start of the month and peaked early last week at $137 a barrel.
"As the oil price has now fallen back, we should hopefully reach the peak and start to see prices going the other way to reflect the big drop in wholesale costs seen at the end of last week, subject to no further spikes in the barrel price this week.
"Drivers should be encouraged by oil and wholesale prices dropping. It's now vital that the biggest retailers who buy fuel most often start to reflect these reductions at the pumps to give drivers a much-needed break from the pain of constantly rising prices."
Figures showed the average price for a litre of petrol at UK forecourts on Monday was 163.7p with diesel at 173.7p, both new records — but it could cost a lot less to fill up in some Northamptonshire towns.
And up the road in Corby, both Tesco and Morrisons were offering 156.7p a litre.
Morrisons was again cheapest in Northampton on Tuesday, 157.9p a litre at the Victoria Promenade forecourt and a penny dearer at 158.9 in Kettering Road.
Tesco's Mereway store still had a litre of unleaded at 157.9p on Wednesday (March 16) — although that was a whopping five pence MORE than it was charging drivers across town at Weston Favell the previous day.
Supermarket prices in Wellingborough remain among the highest in the county with Morrisons' 161.9p the cheapest available on Wednesday (March 16).
Drivers in Daventry, where there are no supermarket garages, face paying up to 162.2p per litre for their petrol — up 11p in a fortnight.
Less than two years ago, in May 2020, a litre of unleaded cost less than a pound as supermarkets engaged in a price war following a crash in global oil prices to 21-year lows.