When the Deepwater Horizon oil rig exploded on April 20, 2010, unleashing a massive oil spill in the Gulf of Mexico, the incident sent shockwaves throughout BP. That included the firm's energy trading floor in Houston, where the focus is more commonly on futures, options and swaps than deep-sea drilling. In May and June that year, as the costs of the disaster mounted, credit rating agencies downgraded the UK-based oil major. Margin calls rained in. Personnel in Houston worked to convince BP's