When most people think of oil, they think of light, sweet crude that comes up out of little holes in the ground. You describe oil by its API gravity. For example, oil like Brent crude or West Texas Intermediate has an API gravity of 38-40. The oil that Col. Drake pulled from the ground at Titusville, Pa., in 1859 had API gravity near 60. These types of oil are relatively easy to pump from a reservoir, lift to the surface and transport via pipeline to the refinery.

The Shift to Heavy Oil, with an “Energy Microsoft” at the Forefront

But a significant portion of the world’s oil is much lower quality than the light, sweet stuff. Indeed, most oil that’s found in nature is a heavy, viscous hydrocarbon with the consistency of cold molasses. This heavy oil - defined as API gravity 22.3 or less - is difficult and costly to produce