Brazil's government is preparing an extra auction this year of stakes in offshore oil areas to boost revenue, a plan gaining steam amid falling oil prices and rising global trade uncertainty, said four people familiar with the matter. Two of the sources, who spoke on condition of anonymity, said the auction will involve smaller, uncontracted parts of the pre-salt Tupi, Mero and Atapu fields, looking to raise around 20 billion reais ($3.4 billion) in a "worst case" scenario. Brazil's Finance Ministry and the Ministry of Mines and Energy did not immediately respond to requests for comment.