The government has launched a new guide encouraged to persuade consumers to switch to the least polluting cars.
As part of the Act on CO2 campaign, the Department for Transport has produced an online guide directing drivers to the greenest cars in each class.
Produced in conjunction with What Car? magazine, the guide is available at Act On CO2.
Drivers can search for the type of car they are looking for - ranging from superminis to 4x4s - and will be automatically recommended the least emitting models.
Transport minister Jim Fitzpatrick said: "Climate change affects everyone and everyone can make a contribution to tackling it.
"By choosing the car with the most fuel efficient engine in its class, drivers could reduce their engine CO2 emissions by 24 per cent and potentially save a quarter on fuel costs.
"So the message is simple - the car you choose can help reduce your impact on the environment, and help save money."
Steve Fowler, editor of What Car? said the rankings would help consumers make an informed choice about the type of car to buy, encouraging them to minimise fuel consumption, save money and tackle climate change.
"Car buyers are making increasingly difficult choices about the cars they buy and these rankings will help them to include environmental factors when making that vital decision," he said.
Friends of the Earth (Foe) welcomed the focus on 'green' choices.
However, Richard Dyer, FoE transport campaigns manager, told politics.co.uk more should be done to offer drivers incentives to choose the cheapest cars.
FoE calls on the government to further increase the vehicle excise duty, recommending car tax for the most polluting cars is raised to £2,000 a year.
In his last budget, Gordon Brown went some way to raise car tax on the most polluting vehicles, but FoE argues this did not go far enough.