With the world awash in crude, the oil industry is contemplating a new problem the oversupply could tee up: an oil shortage. That could leave the world in exactly the opposite situation as now: short of oil and willing to pay more to get it. This may herald the beginning of a cycle that other commodities, from gold to copper, find more familiar—a cycle in which a glut leads to lower prices that lead to investment cuts, which chokes supply and prompts the price gains that lead to renewed expansion and future gluts. “A big gap is forming in oil-industry investment,” Claudio Descalzi, chief executive of Italian energy company Eni E -2.18 % SpA, recently told reporters. “That will lead in two to three years to an imbalance between supply and demand that will push prices higher.” This year, global exploration-and-production investments will fall by $170 billion, or 20%, […]