The shale boom has created a growing problem: America is producing the wrong kind of oil.

Texas and other shale-rich states are spewing a gusher of high-quality crude — light-sweet in the industry parlance — feeding a growing glut that’s bending the global oil industry out of shape.

Refiners who invested billions to turn a profit from processing cheap low-quality crude are paying unheard of premiums to find the heavy-sour grades they need. The mismatch is better news for OPEC producers like Iraq and Saudi Arabia, who don’t produce much light-sweet, but pump plenty of the dirtier stuff.

The crisis in Venezuela, together with OPEC output cuts, will exacerbate the mismatch. The South American producer exports some of the world’s heaviest oil and new Trump administration sanctions will make processing and exporting crude far more difficult. American refiners are scrambling for alternative supplies at very short notice.

Crude isn’t the same everywhere: the kind pumped from the shale wells of West Texas resembles cooking oil — thin and easy to refine. In Venezuela’s Orinoco region, it looks more like marmalade, thick and hard to process. Density isn’t the only difference — the sulfur content is also important, dividing the market into sweet and sour crude. Heavy crude tends to have more sulfur than light crude.

As Saudi Arabia, Russia and Canada cut production, and American sanctions force Venezuelan and Iranian exports lower, the market for low-quality crude is feeling the impact.

“The strength in the physical crude market continues, led by sour crude shortages,” Amrita Sen, chief oil analyst at consultant Energy Aspects told Bloomberg in London, echoing a widely held view within the market.

For consumers and politicians focused on the headline oil price for Brent and West Texas Intermediate, the most popular benchmarks, it may not matter much. Car drivers could even benefit, because too much light-sweet crude often leads to too much gasoline, and lower prices. On the flip side, truckers may find themselves short-changed, as refiners prefer heavy-sour crude to make diesel.

Few oil executives see the market changing soon. The supply and demand balance could deteriorate further as OPEC deepens output cuts next month. At the same time, US shale production keeps growing, feeding the glut of light-sweet crude. The proportion of light crude in US total petroleum output has risen to nearly 57 percent, according to Bloomberg calculations based on US Energy Information Administration data.

In the physical market, oil price differentials for some important varieties of heavy-sour crude — including Russia’s main export grade, Urals, and Mars Blend from the US Gulf of Mexico — are at the strongest levels in five years, according to data compiled by Bloomberg.

Heavy-sour crude is becoming so expensive — and gasoline refining margins are so low — that some US refiners are running their most sophisticated kit at low rates in an effort to save money. Others are likely to follow.