CARACAS, Venezuela -- The driving is easy. The road is smooth. And then, suddenly, the car spins and swirls out of control as it skates along a layer of goo that mysteriously covers highways here.

Venezuelans call the goo La Mancha Negra -- the black stain -- but it's really more like a blob, a thick black sludge with the consistency of chewing gum. No one knows where it comes from. No one knows how to get rid of it.

Some say it's oil from lousy asphalt. Others say it's oil from car engines. It could be burned rubber from frayed tires. Some people think it's all of the above.

Motorists are petrified of the blob.

Government officials are embarrassed and baffled. They've spent millions of dollars studying it, using some of the country's best minds and experts from the United States, Canada and Europe.

They've formed a national commission to study the blob, and even a federal judge is investigating.

"We don't know what it is. We clean it away, and it comes back the next day," said Arturo Carvajal, an engineer and vice president of a company trying to remove the goo from a Caracas highway.

Carvajal's company and a half-dozen others have tried washing the blob away with pressurized water and detergent. They've tried blowing it away with pressurized air. They've tried drying it up with piles of pulverized limestone. And they've scraped it away by repeatedly replacing the top layer of asphalt on some blob-infested highways.

At various times, the government has declared victory, only to have LaMancha Negra return bigger and worse than ever. And it's reproducing, somehow moving from one highway to the next.

The blob also is a killer: More than 1,800 motorists have died in five years on one 8-mile stretch of blob-covered highway from Caracas to the international airport.

"Driving with La Mancha Negra is like driving in a grand prix. You got to be careful, or you'll die," said Antonio Perez, a Caracas taxi driver who frequently deals with the blob.

It was on this road five years ago that La Mancha Negra first appeared. The government was patching up the 30-year-old concrete highway with asphalt when the first shiny blotches emerged.

At first it covered 50 yards. Then 100 yards. And now eight miles.

Many Venezuelans think someone made big money by laying cheap asphalt that bleeds oil when the temperature rises. A judge has been investigating charges of corruption, but no one has been indicted.