On Feb. 1, 2011, oil prices rose above $100 a barrel. For the next three years, they largely stayed there, with few of the dramatic ups and downs that oil markets are famous for. So when prices began falling slowly in June of this year, most industry experts shrugged. Hundred-dollar oil was here to stay, right? That attitude has made the vicious plunge in oil prices over the past few months all the more shocking. U.S. oil production has been rising for several years; more recently, Libyan oil output has surged, too. Those increases collided with a weak global economy this summer to create a glut of oil. Late last month, members of the Organization of the Petroleum Exporting Countries (OPEC) announced that they would not cut their own production to compensate and stabilize prices. Oil promptly fell below $70 a barrel, down 40 percent from its June peak. […]