The chief executive of Brazil\'s state-run oil giant Petrobras, Maria das Gracas Foster, warned Tuesday that the company faces erratic output this year due to platform maintenance. \"2013 is going to be a more difficult year than 2012,\" Foster said in a news conference to discuss the company\'s earnings. Most of the difficulties will come in the first half of the year, she said, because \"we are shutting down platforms\" for maintenance. The situation will be reversed in the second half of the year and production will be increased thanks to six new platforms, she explained. Foster said that Petrobras has projected the same level of production this year as in 2012, which came in at 1.98 million barrels of oil equivalent per day, down 2.0 percent from 2011. After the market closed Monday, Petrobras reported that 2012 net earnings plunged 36 percent from the prior year, to 21 billion reais, or $10.86 billion based on the average exchange rate for 2012. The company cited the depreciation of the real, higher fuel imports and operational costs as the reason for the drop in net earnings.