The news unveiled on the Chinese official visit is a huge boon for Brazil as it endures a fifth straight year of low growth after a period of rapid expansion fueled by an Asian demand for commodities that has since slowed.
Li's host, President Dilma Rousseff, hopes Brazil can direct Chinese cash to overhaul decaying infrastructure as the country's tourist magnet Rio de Janeiro prepares to host South America's first ever Olympics next year.
Brazil's government has been hit by a huge graft scandal embroiling its flagship company over the past year, but the oil giant received a boost earlier this year in signing a USD 3.5 billion financing deal with the China Investment Bank.
Despite becoming Brazil's number one trading partner in 2009, amid an exponential rise in two-way trade, China currently ranks only 12th in terms of actual investment in Brazil, prompting Brasilia to seek deeper economic ties.
Li's tour, aimed at underpinning growing Chinese influence in Latin America, comes just days after Beijing signed accords worth USD 25 billion and USD 22 billion respectively with fellow BRICS developing nations Russia. But the Brazil package is worth more than those combined.
At their talks, aside from the Petrobras agreements, Rousseff and Li also signed a range of deals designed to further bilateral cooperation on trade, investment, agriculture, energy and transport, official sources said.
Vale said it would expand an existing accord by selling four ore carriers to China Merchants Energy Shipping Co. Ltd without giving a figure for the agreement.
Further topics on Tuesday's agenda ranged from lifting an import ban on Brazilian beef and also an ambitious project to build a railway from the key southeastern Brazilian port of Santos more than 3,500 kilometers (2,200 miles) to the Peruvian Pacific port of Ilo.