Only 52% of web users are able to find the correct CO2 emissions figure for a car, according to a new survey.
Then, when users are able to find an emissions figure just 68% of these are correct.
The research looked at how easy it was to find CO2 information on manufacturers' websites, and was conducted for the Energy Saving Trust, Friends of the Earth Europe and We Are Futureproof.
The disparity in clear access to CO2 figures was demonstrated by web users taking 74 seconds on average to find CO2 figures on Lexus's website, compared with nearly eight minutes on Alfa Romeo's site.
Fuel economy labels aren't used
The Fuel Economy Label, which includes CO2 emissions and other related information, rarely appears on manufacturers' websites, and accounted for just 5% of successful emissions searches.
It's compulsory for car showrooms to display fuel consumption and CO2 data, but not for websites where finding this information was described as 'like looking for a needle in a haystack.'
The Energy Saving Trust is calling for car manufacturers' websites to use the fuel economy label next to every model. It estimates Britons could save over 500m and 1.2 million tonnes of CO2 through buying more efficient cars.
Clean car data no easier to find
The study found no link between how easy it is to find a car's emissions figures on the manufacturer's website, and how clean the car is. This means that the cleanest car companies are missing an opportunity to promote this.
However, the overall ease of use of a website was directly linked to how quickly users were able to find emissions figures.
The best and worst car websites
Mini, Kia, Lexus and Honda performed best in delivering CO2 information quickly and accurately, according to the report.
The worst sites in descending order were Mercedes-Benz, Smart, Nissan and Alfa Romeo.