Malaysian State oil company Petroliam Nasional has started inviting bids for its upstream assets in Africa, which could fetch as much as $3-billion, people with knowledge of the matter said. Petronas is working with an adviser to gauge interest in the portfolio, which includes operations in Chad, according to the people, who asked not to be identified because the information is private. The assets are likely to attract other international energy companies or financial investors, and could be sold piecemeal to different buyers, the people said. The Malaysian firm has also been considering options for its downstream assets in Africa, though it hasn't decided how to proceed, two of the people said. Deliberations are at an early stage and there's no certainty they'll result in a transaction, the people said. Petronas has upstream projects in countries including Chad, Egypt, Gabon, Gambia, Senegal and the Republic of South Sudan, according to its website. The company said in an emailed statement that it "regularly and proactively" reviews its entire portfolio to ensure it remains resilient amid the evolving energy landscape.