Pre-Salt Petroleum, a government agency tasked with selling oil handed over to the Brazilian state, has released a tender seeking a firm to market the crude it receives from the nation’s offshore Tupi field, it said March 31.

In Brazil, oil and gas firms operating in the so-called “presalt polygon” are typically required to hand over a portion of their production to Pre-Salt Petroleum, as a condition of their exploration and production concessions. The presalt polygon is a large area off the coast of southeastern Brazilian where billions of barrels of oil are trapped beneath a layer of salt under the ocean floor.

Operated by state-run Petrobras, Tupi produced 920,000 barrels per day of crude in January, according to data from Brazil’s oil regulator, though only a small portion of that goes to Pre-Salt Petroleum, commonly known by its Portuguese initials PPSA. Royal Dutch Shell and Petrogal, controlled by Portugal’s Galp Energia SGPS SA, hold minority stakes.

Eligible bidders will participate in an auction scheduled for April 28. The winner will be responsible for marketing 4 million barrels of oil, worth an estimated $218 million, PPSA said in a statement.

Offshore