Oil prices are down than more than 25 percent since June and are staying low for now. Drivers may appreciate that, but for oil companies, it's making some of the most controversial methods of producing oil less profitable — and in a few cases, unprofitable.

Most of the world's oil is selling for about $80 to $85 a barrel now. But not all oil is created equal. In the Middle East, it's cheaper to produce, at a cost of less than $30 a barrel on average, according to the Norwegian firm Rystad Energy.

But in the Arctic, producing a barrel costs $78 on average. From Canada's oil sands, it's an average of $74 a barrel. And because those are averages, some companies have costs that are higher — which means there could be drillers currently producing crude at a loss.

Here in the U.S., the oil drilling boom is due largely to technologies like hydraulic fracturing, or fracking, used to force oil from shale formations deep underground. Producing this oil, Rystad figures, costs an average of $62 a barrel.

"What is really interesting for the U.S. drillers and producers is how long they are going to continue the high activity levels that they have, now that prices are going down," says Per Magnus Nysveen, head of analysis at Rystad.

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