Currently refiners are benefitting from that spread because they're able to buy US crude oil at the lower prices, refine it and then sell their products at levels based on the higher priced Brent.
"That might sound like you're being ripped off," said Cramer, "but the truth is it's just how business works. Once the oil is refined, these companies have the right to sell their product anywhere. It is, alas, a global market, and if you don't want to pay for gasoline that's priced off of Brent, there are plenty of people around the world who will."
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As if that weren't enough, the refiners have another thing going for them. The nature of the refining business is such that it's almost impossible for a new competitor to break into the industry.
"That's because in the United States there are simply enormous barriers to entry," Cramer said. "From an environmental perspective, it's incredibly difficult to get approval to construct a new refinery—just getting a permit from the government can take many years, especially since no one wants a refinery in their backyard."
According to Cramer's research there hasn't been a single new refinery built in the United States since 1976.