"Fuel additives are one of the cost-effective ways to get engines to do what they were designed for," Patrice Bres, head of the special fuels division of Europe's top refiner Total PA, told the Asia Oil and Gas conference.

He said the move to lower-sulphur diesel, with the European Union now requiring a maximum of 0.005 percent sulphur, caused a problem with high pressure fuel injection engines, but this could be overcome through additives.

Asian countries are following suit to cut sulphur since it is blamed for acid rain and lung problems.

This is leading refiners to build hydrocracker units with price tags in hundreds of millions of dollars, and also need hydrogen gas supply to help remove sulphur.

"It all requires a lot of hydrogen, more conversion and more investment," said Norm Gilsdorf, senior vice-president of technology firm UOP LLC.

"Hydrogen is the most expensive feedstock and demand is increasing rapidly," he said, adding that new technology was needed to improve the recovery and life cycle for hydrogen use.

Total says hydrogen supply availability will limit the number of refineries that can build hydrocrackers in Europe, where diesel demand is climbing.

"The refining industry's challenge is to balance the supply and demand of motor fuels while coping with the automotive industry's quality requirements," Bres said.

"You have to do that while minimising the impact on the environment, which is becoming a more stringent constraint."

He said the world's car population would soon reach one billion, with road transport contributing 40 percent of CO2 emissions, now capped in the EU by UN Kyoto Protocol commitments.

Bres said Total had started marketing a diesel additive that converts around 85 percent of pollutant nitrogen oxide to water vapour and nitrogen, and another to reduce noise pollution.