To understand the immense scientific challenge that separates the Orinoco's "heavy oil" from your car engine, consider for a moment the mechanics of conventional oil production. Forget all those diagrams of big black pools being tapped by wells. A "reservoir" of oil is not a pool -- it is an underground field of rock porous enough to trap in small cavities the ancient, decomposed plant and animal matter we call oil.

In an ideal field -- where the oil is light and the rock that holds it contains enough loose spaces for the oil to flow -- oil workers start a well by drilling a long hole and then dropping a hollow cylinder straight into the rock.Then they blow holes from inside through the walls of the cylinder.

The deep underground rock is under a lot of natural pressure, and the sudden difference between the pressure in the rock and the pressure in the tube may force the oil right into the cylinder and up out of the ground. If there is not enough natural pressure difference, then a mechanical pump sucks the oil up, just like a traditional water well.

Now imagine trying to do that with oil that has the texture of blackstrap molasses. Underground, where it's hot, the oil flows so thick and slow that most wells cannot naturally produce enough to make it pay. And if you've ever seen molasses that has been in the refrigerator for a while, you can picture what happens to the oil when it reaches the cooler air near the surface. You could scoop it into a paper cup, turn the cup over, and have a pleasant conversation before the oil even started working its way toward the lip of the cup.

The best way to make this oil flow at a reasonable pace is to heat it up while it still sits in the rock. There are various ways to get that heat underground, but in the Orinoco heavy oil belt they have decided to do it by shooting steam straight into the rock through underground pipes. They can "steam soak" individual wells this way, or they can place a steam injector -- sort of a glorified fire hydrant -- in the center of a circle of wells, and hope that as the underground oil around the injector heats, the oil is flowing slowly through the rock and toward the pumping wells.

To make all that steam, you need boilers, holding tanks, mazes of pipes, water pumping systems -- a whole industrial plant for each heavy oilfield. But once the oil is out, things get even more complicated.

If it cools off, it congeals. So the producers can transport it in heated pipelines, store it in heated tanks, ship it in heated tankers -- an enormous expense. Or they can dilute it with some lighter substance, like kerosene. But then they have to separate out the diluent at the refinery, and they need a whole new pipeline to get the diluent back to the oil field.

Then to refine heavy oil, they have to literally break the molecular structure apart. All crude oil is a molecular hodgepodge -- hydrogen and carbon, its two basic elements, link together in different random combinations. One molecule will have one carbon atom to four hydrogen atoms. Another will have one carbon to fifty hydrogens.

Hydrogen is by far the lighter element. Molecules that are rich in hydrogen make a gasoline, the lightest and most desirable of the liquid crude oil products. A little heavier -- less hydrogen, more carbon -- and you get fuel oil. Heavier still is asphalt. If under the right conditions you apply heat and chemical catalysts to a conventional crude, which contains a mix of all these, the various products will separate out as the temperature rises -- and that is the essence of refining.

The molecular range varies in every crude, but the greater the proportion of light molecules, the lighter the oil -- and the more gasoline it produces. So one of the problems of refining heavy oil is that you wind up with far too much asphalt and fuel oil, and not enough gasoline.

Scientists have discovered that if you physically break the carbon loaded molecules that make up the heavier products -- a special heat-and-pressure procedure called "cracking" -- you can pull out some of the carbon atoms. The leaves a better proportion of hydrogen, which means more light products, but it also leaves a lot of pure carbon lying around.

Pure carbon is coke, a black coal like substance that sticks to the side of the vessel. The oil people have to figure out a way to remove the coke and then, ideally, find some use for it, like burning it as a source of energy. aThere are various techniques for doing that now, bur some of them are quite new, and still untested on the Orinoco oil. And it means yet another expense.

One other major refining problem for the Orinoco oil is that the oil is loaded with sulfur and other minerals. The minerals tend to neutralize the chemical catalysts used in refining, so they must be removed before the refining can begin. And since existing refineries are designed to handle certain types of oil -- most are specifically geared to much lighter crudes -- whole new plants will have to be built to accept the Orinoco heavy oil.