After years of deep exploration and almost $10 billion in investment since 2009, Petroleos Mexicanos (Pemex) made a big oil find in the ultradeep waters of the Gulf of Mexico. Pemex is preparing to announce a second deepwater discovery in coming days, according to company executives. The finds will bolster the legacy of Mexican Pres Felipe Calderon, who had overseen declines in crude output by Pemex every year since he took office in late 2006. But ultimately the discovery could derail an overhaul of the company promised by President-elect Enrique Pena Nieto, who assumes office on Dec 1. Nieto promised to change rules that allow private and foreign oil companies to provide services to Pemex but ban them from owning stakes in Mexico's oil and gas fields.