Motoring costs are never far from the front page and most buyers want to save at the pumps but, with every automaker claiming to offer fuel consumption lower than the rest, where do car buyers start?In the latest of its regular Data Bank features, www.honestjohn.co.uk in Britain has the answer after rounding up the 10 most fuel-efficient new cars on the market to help buyers get the best value for money in a tough climate.PROVING A HITAll the cars in the list - not surprisingly - have a diesel engine and CO2 emissions below 100g/km.Best of the lot is the Kia Rio Ecodynamics - new on the UK market in September 2011. Its 1.1-litre diesel engine delivers a claimed 3.12 litres/100km, along with a decent power output 55kW and 169Nm of torque. Not only that but it has four-doors-and-a-hatch, five-seat practicality and a seven-year/160 000km warranty (in Europe) so it’s clear why it’s proving a hit with cash-savvy buyers.Second is the Smart Fortwo CDI diesel with a claimed fuel consumption of 3.3 lites/100km. It’s only a two-seater but, thanks to its tiny dimensions, it’s the ideal car for town – so finding a parking space won’t be a problem. It’s not the most powerful car – the 800cc engine produces only 40kW but in the city outright performance doesn’t really matter.Just behind the Smart is the C3 1.6 e-HDi Airdream, which has arrived in Citroen showrooms in just the past few weeks. It’s more expensive than the Fortwo and the Rio at £15,290, but there are a few nice extras - like a panoramic windscreen – to add to its appeal. The 3.34 litres/100km fuel economy figure is owed in part to a start stop system, which saves fuel when the car is stationary by cutting the engine. IMPRESSIVE ON PAPERThe Skoda Fabia (Skoda doesn't sell in SA) comes in fourth. The 1.2-litre TDI engine in the Greenline II is shared with two other cars from the top 10, including the fifth-placed SEAT Ibiza Ecomotive, but it delivers the best economy when fitted to the Fabia, matching the C3 with 3.34 litres/100km. The sporty looking Ibiza is just behind, with a claimed 3.5 litres/100km. The Honest John list also includes the Vauxhall Corsa ecoFLEX and VW Polo BlueMotion (each 3.5 litres/100km, the Alfa Romeo MiTo JTDm-2 (3.6/100), the Citroen DS3 e-HDi Airdream (3.6/100) and the Ford Fiesta 1.6 Econetic (3.6/100).It’s worth noting that these fuel consumption figures are all the official figures – the only ones that manufacturers can legally quote. In reality, drivers are reporting different data in the Honest John Real Life Fuel Economy Register, which averages readers' fuel consumptionsubmissions to deliver a clear picture of what buyers can actually bexpect from their car.Nonetheless, these 10 models do offer impressive economy on paper.Daniel Harrison, editor of www.honestjohn.co.uk, said: "Fuel consumption has become a key selling point in recent years and every automaker makes a claim of some sort. It can leave buyers baffled, so this list clearly sets out the nation’s cleanest cars."The Honest John Top 10 fuel-efficient cars according to the manufacturers' published figures (litres/100km):1 Kia Rio Ecodynamics - 3.122 Smart ForTwo CDI - 3.33= Citroen C3 e-HDI Airdream; Skoda Fabia Greenline II - 3.345= SEAT Ibiza Ecomotive; Vauxhall Corsa Ecoflex; VW Polo BlueMotion - 3.58= Alfa Romeo MiTo JTDm-2; Citroen DS3 e-HDI Airdream; Ford Fiesta Econetic - 3.6Data Bank features are a regular feature on www.honestjohn.co.uk/specs with further Top 10 lists covering various criteria from insurance groups and interior space to performance and dimensions.