The research, from What Car?, found that the Mercedes-Benz C300e was the most fuel-efficient car currently on sale in the UK. The vehicle averaged a massive 470.8mpg in official WLTP fuel consumption and emissions tests.
The C300e, a plug-in hybrid, can also travel up to 62 miles purely on electric power.
Widespread availability of hybrid and plug-in hybrid vehicles (PHEVs) means some of the latest cars are capable of stunning fuel efficiency.
Luxury brands dominate the top of the chart with Mercedes-Benz, Volvo, Land Rover and Lexus occupying the top four places.
The cars from the top 10 brands come from a range of classes – everything from family hatchbacks to luxury SUVs.
What Car? editor Steve Huntingford commented on the data, saying drivers were in a tough position with the rising fuel prices.
He said: “Given the rising cost of living, things like fuel economy are an increasingly important consideration for car buyers.
“The good news is modern PHEVs, in particular, are capable of incredible efficiency if you do mostly short journeys and plug them in regularly.”
The latest data from RAC Fuel Watch shows that drivers are paying an average price of 188.74p per litre of unleaded petrol, although prices “should fall”.
Diesel drivers are slightly worse off, paying an average of 196.36p for a litre, as the RAC predicts that further cost increases are likely.
Super unleaded petrol has broken the £2 barrier, with those opting for premium fuels seeing costs of 200.25p per litre.
RAC fuel spokesperson Simon Williams said: “The average price of petrol went up yet again on Sunday to a new record of 188.7p a litre.
“More than five weeks of successive record prices has caused a litre of unleaded to rocket 23p from 165.5p in mid-May.
“This is yet more bad news for drivers, particularly with this week’s rail strikes leaving many people with no choice but to use their cars.
“But looking at the wholesale cost of petrol, which has settled due to the falling oil price, petrol pump prices really should not continue to rise, if anything they ought to begin reducing.
“Sadly though, diesel looks destined to head rapidly towards an average of £2 a litre which would make a full tank £110.
“We strongly hope the extent of the rises seen in both fuels will finally force the Government to take action to ease the burden on drivers by further cutting duty or lessening the punishing impact of VAT which currently accounts for 31p a litre on petrol – 6p more than it was before the Ukraine war began.”
The Competition and Markets Authority (CMA) is currently conducting an “urgent review” into the fuel prices.
The top 10 most fuel-efficient models by brand
Mercedes-Benz C300e – 470.8mpg
Volvo S60 Recharge T8 PHEV – 403.0mpg
Land Rover Range Rover Sport P440e – 341.2mpg
Lexus NX 450h+ – 319.9mpg
Volkswagen Golf 1.4 TSI eHybrid – 319.9mpg
Skoda Octavia 1.4 TSI iV – 282.5mpg
Toyota RAV4 2.5 PHEV – 282.4mpg
Suzuki Across 2.5 PHEV E-Four – 282.4mpg
Peugeot 308 1.6 Hybrid 180 – 281.1mpg
Ford Kuga 2.5 PHEV – 257.0mpg