The United States is finding itself in a strange situation, where the bounty of so much unconventional crude oil is not yet manifesting itself at the refineries.

Simply put, US refineries, especially those in the Gulf Coast are better suited for the heavier, more sour crudes from places such as Mexico and Venezuela.

The U.S. hasn’t built a new oil refinery in at least 30 years, and the existing fleet in many cases reconfigured their plants to cope with the more heavy sour crudes that have been available in the international market. But the crude oil from places such as Eagle Ford in Texas are creating a problem for those refineries.

We are hearing reports that refineries are now spending capital on a “first wave” of modifications - mods which will bring quick returns for low investment. The next wave requires much larger investment and therefore a greater level of confidence that the shale boom and its flood of light sweet crude will continue for the full investment horizon.

Valero, which processes about 2.4 million barrels per day of crude across 10 refineries in North America, is gradually processing more light U.S. crude. The firm plans to spend about $750 million on two new refineries that will better handle oil from the Eagle Ford field.

“What you’re seeing is that as more of this light crude becomes available, there’s plenty of ability for North American Refineries to process it,” a spokesman for Valero told CNBC. He added that the company now processes about 50 percent light sweet crude, up from 1/3 just five years ago.

“Valero’s Gulf Coast refineries have stopped importing light sweet crude internationally because there is so much available domestically,” he added.