By Tom Symonds
Transport correspondent, BBC News
Vehicles set off on the 400-mile route of the MPG Marathon from Bristol
Teams of drivers have started a two-day motoring rally across the country - but the winner is not necessarily the first vehicle over the finishing line.
Four hundred miles of beautiful British countryside using as little fuel as possible: That's the challenge for the competitors in the MPG Marathon.
It's being held to show how much fuel people can save if they alter their driving habits.
We started out at 10.30am from Bristol, a shiny collection of mainly small cars with the odd police Cruiser and Corvette thrown in.
The BBC was travelling with the AA entry co-driven by its president Edmund King.
"When we asked motorists what they considered doing to help the environment, 60% said they'd consider eco-driving," he said.
"I do think people are conscious of this issue and the price of fuel has brought it to the fore. People are already driving more slowly, particularly on motorways.
One of our rival competitors, the former rally driver James Sutherland, is the man to beat.
In a previous fuel marathon he managed to get 83 miles to the gallon out of his car, a perfectly normal diesel Toyota Aygo.
The secret, he says, is to stay off the brakes and be as smooth as possible on the accelerator.
Instructors that teach eco-driving advise getting into a higher gear as soon as you can and being aware when you can ease off while going down hill.
They also recommend proper footwear for the job, thin-soled shoes through which you can feel the accelerator pushing on your feet.
Our route takes us through the Wye Valley, across the midlands to the Peak District and Stockport before returning to Bristol via the Brecon Beacons mountains.
It's not easy driving. We are finding it hard not to burn fuel as we labour up some of the steeper hills.
By 1500 on Day One our average fuel consumption was a not-embarrassing 71 miles per the gallon.
That is only a touch over what the manufacturers of our Fiat 500 say is possible and some way behind the 81 mpg claimed by a fellow competitor. But the race isn't over yet.