Malaysian state-owned oil and gas firm Petronas is aiming to sell a large minority stake in a prized upstream local gas project for up to $1 billion as it seeks to raise cash and cut development costs, two sources familiar with the matter said.Petroliam Nasional (Petronas) is looking to sell a stake of as much as 49 percent in the SK316 offshore gas block in Malaysia's Sarawak state, the sources told Reuters, a move that would be among its first major recent sales as it grapples with oil prices that have slumped by half over two-and-a-half years.