Dozens of American shale oil companies could go bankrupt. That's as prices reach a historic low.

Some experts believe 100 oil and gas companies could file for bankruptcy this year if prices don't go up significantly.

The companies use hydraulic fracturing to get shale oil out of rock and stone. The innovative method has made the United States a major oil producer. But, it's expensive.

West Texas Intermediate Crude is the cheapest it's been since the New York Mercantile Exchange started trading oil futures.