A sharp rise in heating oil prices is fuelling concern among MPs.
Kit Malthouse, Conservative MP for North West Hampshire, has joined more than 50 Tory MPs in calling on the Competition and Markets Authority (CMA) to investigate possible profiteering.
The MPs allege suppliers are exploiting rural, off-grid households across the country.
Mr Malthouse said: "Heating oil customers are being ripped off while the government sits on its hands.
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"Many families in rural communities across NW Hants have no choice but to heat their homes with oil, and some suppliers appear to be taking advantage.
"I've heard from constituents who were quoted a price, only to be told it was a 'floating price' with the final cost not confirmed until the order was placed and paid for.
"One constituent saw the price for 500 litres rise by 170% in under a week.
"In many areas there is only a single supplier, and they are under no legal obligation to publish their prices, leaving customers unable to compare costs or shop around.
"That lack of transparency makes it far too easy for households to be charged inflated prices.
"I hope the Competition and Markets Authority investigates this and steps in to protect consumers, because right now the government is doing nothing."
In their letter to the CMA, the MPs described "blatant profiteering" and "price gouging," citing reports of suppliers quoting prices that later doubled before delivery, as well as deliveries cancelled and reissued at higher prices.
The issue follows a recent surge in global oil prices linked to conflict in the Middle East, which has quickly filtered through to UK heating oil costs.
However, MPs argue the scale and speed of increases suggest unfair pricing.
Around 1.7 million UK homes, mainly in rural areas, rely on heating oil and are not covered by the domestic energy price cap.
Off-grid households often have little choice of suppliers, with many areas served by just one or two companies.
This limited competition, combined with a lack of published prices, leaves consumers without the ability to compare costs or switch providers easily.
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