Experts at Which? Car tested three of the most popular superfuels - Shell V-Power, Tesco Super Unleaded and BP Ultimate Diesel against standard fuels.
Their report concluded that there was 'little justification for using them'.
It added: 'Superfuels are more expensive at the pumps but advertisers often claim they can optimise a car's economy and increase power.'
The Which? Car report found that a Ford Focus 1.6 running on Shell V-Power had a 'a marginal power increase'.
But filling the car on this petrol for 12,000 miles will cost drivers £1,892 - or £116 more than using Shell's standard petrol (£1,776).
It noted that Tesco Super Unleaded 'actually decreased the power of the Focus' though economy did improve by 0.41mpg (1.2 per cent).
The report concluded: 'Despite the marginal power increase offered by Shell's V-Power petrol, there seems little justification for using superfuels over their regular counterparts.'
A Volkswagen Golf's hi-tech 1.4 TSI engine responded well on Shell V-Power, but there was 'little to choose' between the superfuels and ordinary petrol on gains in economy and emissions, despite costing £89 a year more.
A Renault Megane 1.5 diesel's economy and performance of were 'both slightly worse' using BP Ultimate diesel, the super fuel furthest from the marketing claims in the test - despite costing £84 a year more.
The report concluded: 'Each superfuel had only a marginal effect on the emissions of measured pollutants, seemingly putting paid to environmental claims.
oke:
