Tupi pre-salt field, Brazil

The Tupi oil field lies in the Santos Basin, about 250 kilometres off the coast of Rio de Janeiro, Brazil. The Brazilian company Petrobras discovered it in October 2006, and it is one of the biggest oil finds in the Western Hemisphere in decades.

The oil is trapped in rock beneath a thick layer of salt, under about 2,000 metres of seawater. That is why it is called pre-salt oil. The field is also known by the name Lula, which means squid in Portuguese. The discovery showed that large amounts of oil can hide deep below the ocean floor, and it made Brazil one of the world's important oil producers.

Why is it called pre-salt oil?

Millions of years ago, a thick layer of salt formed above the rock that holds this oil. Today the reservoir lies below about 2,000 metres of ocean water and then roughly 5,000 metres of salt, sand and rock. The salt layer is more than 2,000 metres thick in places. Reaching oil buried so deep was a major engineering challenge.

How big is it and who runs it?

Petrobras operates the block with a 65 percent share, and two partners hold the rest. The field holds at least 5 billion barrels of recoverable oil, which could raise Brazil's reserves by about 62 percent. It was first named Tupi after the Tupi people, renamed Lula in 2010, and later reverted. Oil is produced through floating ships that process it at sea.

On the globe

The model shows the offshore production ships over the oil field, in the open sea.