The automobile engineers said they had noticed the rise in 'oil volumes' in all vehicles about three years ago.

The problem became alarming about a year ago when new cars started to break down due to 'increasing oil in the engines', they said.

When diesel, kerosene or CNG condensate (a by-product of gas fields and CNG filling stations) are unscrupulously mixed with petrol and octane, the fuel fails to properly burn.

The unburnt substance sips into the engine through the piston seals. This increases the lubricant level and also lowers down the viscosity of the oil, turning it much thinner than needed.

Leading lubricant suppliers had conducted several tests in the wake of complaints by car importers, workshop owners and motorists.

The tests found the level of adulteration was up to 20 percent in petrol and octane sold in the fuel stations.

In most of the cases petrol and octane are adulterated at various levels in the chain of import and distribution to make undue profit.

Automobile experts say fuel adulteration is also causing 'national loss of hundreds of crore of taka' for spare parts, most of which are imported in foreign currency.

They say the vehicles are also emitting additional toxic gas due to adulteration, causing serious air pollution in urban and rural areas.

The level of adulteration is so high outside the capital that thousands of vehicles regularly break down there.

Some of the top garages and car dealers had even sought help from Japanese car manufacturers, who dispatched an expert delegation. The Japanese experts have also confirmed fuel adulteration is the cause of trouble in the vehicles.

The delegates said they could not help check the problem. But they advised motorists to regularly check oil volume and manually drain out excess oil.

Automobile experts also suggest changing the oil after every two periods of drainage.

Bangladesh Petroleum Corporation (BPC) sources say Bangladesh imports about 120,000 tonnes of octane and 1.4 million tonnes of crude oil every year.

Theft of octane begins at the port city of Chittagong by certain organised cliques. Further theft and adulteration occur throughout the chain of distribution to about a dozen depots across the country from the Chittagong refinery.

A third round of adulteration takes place when tank lorries carry the fuel to thousands of stations across the country.

Gas condensate sold by Petrobangla from the gathering stations of its eight operational gas fields at Tk 13.09 per litre is the most preferred ingredient for adulteration, the BPC sources say.

Petrobangla alone produces about 3,800 barrels each containing 159 litres of gas condensate a year to be used for various industrial purposes.

Bangladesh Standards and Testing Institution (BSTI) is responsible for monitoring the market.

Fuel station owners allege BSTI inspectors regularly extort money from them. They demand that the inspectors should clamp down on unscrupulous workers at the depots, tank lorries and port areas.

"If suppliers provide us with adulterated fuel what can we do? We don't have any alternative or we can't man all the points where adulteration takes place," said a fuel station manager on Mirpur Road.

He claimed his pump had just paid a fine of Tk 5,000 to BSTI officials, who found 'adulterated' octane at the station.

Contacted, Lutfor Rahman Khan of Certification Marks department of the BSTI declined to comment.