TRANSPORT company Stagecoach is to adopt a fuel-saving compound across its entire bus fleet after tests showed it reduced usage by more than four per cent.

The group said results of a three month test of the Envirox catalyst - produced in Oxfordshire - demonstrated a 4.3 per cent fuel saving.

Perth-based Stagecoach, which also operates the Oxford Tube and services across the city as well as other routes in scores of towns and cities, started using the diesel additive in 2004.

A validation test was then carried out last year for 550 vehicles in the North West of England, demonstrating the 4.3 per cent saving.

Adrian Havlin, Stagecoach's group technical engineer, said: "Our vehicles have driven more than 700 million miles on Envirox, and to achieve a consistent result across a diverse fleet over three years testifies to the robustness of the technology.

"We are particularly pleased with the performance of the product both in ultra low sulphur diesel and in blends containing biodiesel, which are now in widespread use across our fleet."

Shares in Kidlington-based Oxonica, which makes Envirox, more than doubled after yesterday's announcement.

The catalyst lowers the combustion temperature of carbon in the fuel, helping to burn away harmful chemical deposits from the engine that inhibit performance. It means more power gets transferred to the crank shaft.

Oxonica, which is three per cent owned by Stagecoach, said other positive test results for Envirox had been achieved on mainland Europe.

A recently completed bus trial in Italy demonstrated fuel savings of 10.6 per cent after six months and 10.6 per cent after 6 months, the firm said, with other trials in Germany demonstrating savings of between five and eight per cent.

Oxonica's chief executive Dr Kevin Matthews said reducing diesel fuel use by five per cent in the UK would save three million tonnes of carbon dioxide per year.

He said: "The evidence for the performance of Envirox is becoming increasingly compelling at a time when the issues of climate change and high fuel costs are becoming acute.

"This proven technology offers the potential to make a real difference to carbon dioxide emissions today."