Crude oil has risen by 25 percent over the last three weeks, which has helped energy to be the best-performing sector this month, outperforming the by more than 2 percent.

But not every energy name is along for the ride.

Refining companies like Valero and Tesoro have gotten hit hard over the past week, falling 8 percent and 6 percent, respectively. This is because refiners buy crude oil to make into gasoline, but wholesale gasoline prices have not risen nearly as quickly as oil has over the past week. So these companies are now seeing their costs increase, but aren't bringing in much more revenue.

"I think this has been a hiding place for investors. When oil's coming in, the refiners benefit. And people put a lot of money in here, and they watched. Now that you're seeing this trade stabilize a bit in terms of crude, you're seeing money flow out of these names into other areas of the space," said David Seaburg, head of equity sales trading at Cowen & Co.

And Seaburg says it could get much worse for these names.

Looking at Valero specifically, Seaburg predicts that "as it overshot to the upside when oil was getting crushed, it's going to overshoot to the downside here."

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