Private-equity firms fueled the US shale revolution with $125 billion. Now they face a reckoning of epic proportions as the oil market melts down.

· The US shale revolution that propelled the country to energy dominance was backed in large part by private-equity firms. 
· Now, many of those firms may be at risk as the price of oil reaches 20-year lows and fuel demand evaporates.
· Small to midsize firms that specialize in oil and gas will have trouble raising funds in...