Betting that oil prices were about to crash was an audacious wager, one made all the more remarkable by the individuals behind the deal—civil servants with unassuming titles such as “director general of fiscal planning.” In the lucrative oil business, a profession known for its generous compensation, these government employees were probably the worst-paid stiffs around. Yet the men from Hacienda—so called still, even though women are sometimes in the room—proved prescient in predicting a crash. ... In December 2009 the four investment banks involved in the deal wired the proceeds of the wager back to Mexico. Official records tracking the money that landed in Account No. 420127 at state-owned Nacional Financiera bank show the tidy sum Mexico made: $5,084,873,500. ... Despite its size, impact, and huge fees, the deal is one that few people, even in the energy industry or on Wall Street, know much about. Painstakingly, the world’s 12th-largest oil producer and its bankers have cloaked the program in secrecy to prevent others—namely trading houses and hedge funds—from front-running Mexico’s orders.