A fleet of "poo-powered" council vans are now being driven in Sheffield.
They are part of an attempt by the city council to encourage sustainable motoring as a "practical alternative to petrol and diesel".
The six vans run on biomethane gas generated from sewage treatment works. It produces gas, which is compressed, cleaned and turned into fuel.
Despite being powered by fuel created from sewage, the vans do not smell unpleasant.
Kelda Water Services and its sister company Yorkshire Water are supplying the council with the biogas, which is produced at their sewage treatment works in Sheffield.
Paul Kelly, of Kelda Water Services, said: "It is a sustainable power. It is going to be around for as long as we are around.
"We have plenty of it and we have the process and technology to turn it into poo power, in terms of the trial."
Councillor Shaffaq Mohammed, of Sheffield City Council, said: "One of the big things we have is a number of vans going around the city delivering services.
"So we looked at how we could reduce our carbon, and working with our partners we realised there was alternative technologies available, and bio methane is one of them."