A four-day strike against Petrobras gathered steam on Wednesday, cutting crude and natural gas output from the No. 2 South American oil producer and threatening to become the most disruptive walkout at the state-run oil company in 20 years. Petroleo Brasileiro SA, as Petrobras is formally known, is expected to continue to report significant output cuts after new offshore units were affected by the strike, which began on Sunday. On Monday Petrobras said it had lost 273,000 barrels a day of crude output, or about 13 percent of its Brazilian output. It has made no formal estimate for output since then. The cuts have already caused the biggest strike-induced hit to Petrobras’ crude output […]