Abu Dhabi has rationed the supply of diesel to heavy duty vehicles at its petrol pumps to ease worsening traffic congestion on main streets and prevent a possible supply shortage because of surging demand, suppliers said yesterday.

Diesel sales at the emirate's petrol stations to trucks and other medium and large vehicles have more than doubled over the past six weeks following a decision by retail fuel suppliers in Dubai to raise prices for the eighth time in nearly a year.

The decision has prompted most trucks to head for Abu Dhabi to fill their tanks to take advantage of a price gap of more than Dh10 per gallon as Abu Dhabi has left its diesel prices unchanged during that period despite sharp rises worldwide.

Abu Dhabi's state-owned fuel supplier Adnoc told its more than 100 petrol stations this week that diesel supplies most not exceed Dh200 for large trucks per day and Dh100 for small and medium vans and buses.

"There has been a rush by those vehicles at our stations and this has created a pandemonium at the stations and on the streets," an Adnoc source said.

"The police could not do anything to resolve this problem so we had to step in… from now on, the maximum limit of diesel supply for each large truck is Dh200 a day and for smaller vehicles is Dh100 a day… we have instructed all our stations to comply with these rules as they will also curb the rush for supply and prevent any shortages," he said.

Despite the new decision, long queues of trucks and buses were still seen at petrol stations and surrounding streets this week inside and outside the capital.

Service employees said the large gap in diesel prices between Abu Dhabi and Dubai is prompting drivers to take the trip to Abu Dhabi.

"There is a difference of more than Dh10 per gallon and this means a truck can save about Dh100 per each 10 gallons. We are having a real problem not only due to traffic but the mess these vehicles are creating at the station," said an employee at an Adnoc petrol station.

"Many of them are rushing and pushing… they are not disciplined and this is affecting other cars that come for petrol… many of these cars are turning away because the entrance is sometimes blocked by the big vehicles."

Responding to a police request, Adnoc decided last week to restrict diesel supply to trucks to two stations inside the capital on the grounds they have enough space and a separate diesel service facility. The remaining trucks have to head for Musaffah industrial city just outside the capital.

"Police patrols come here many times every day to watch the situation but it seems they cannot do anything apart from organising the queue," said the worker.

In their latest decision, Dubai-based oil retailers – Emarat, Emirates National Oil Company (Enoc) and Emirates Petroleum Products Company (Eppco) – decided last month to increase their diesel prices by 75 fils to push up the price of a gallon to Dh19.25, one of the highest levels in the world.

Within 18 months, diesel prices have more than doubled from Dh8.35 in January last year.

Adnoc, which controls Abu Dhabi's massive hydrocarbon sector, said it would not change its subsidised price of Dh8.60 per gallon, less than half the Dubai price.

Traders attributed the widening gap to the fact that Dubai-based companies get their oil from the international market, where crude prices have rocketed above $145 a barrel. In contrast, Adnoc supplies its refineries with crude produced by its own companies.

The latest increase in diesel prices came amid a surge in inflation rates and in domestic fuel consumption in the UAE because of an economic upswing.

From around 63,000 barrels per day in 2001, diesel demand in the UAE leaped to 94,000 bpd in 2006 and was expected to have exceeded 100,000 bpd in 2007.

Consumption is projected to surge this year due to a sharp growth projects to maintain the country's position as one of the biggest energy consumers relative to its population.