BP PLC (BP) said Tuesday it has bought stakes in four deepwater oil-and-gas exploration areas off Brazil 's northeastern coast that geologists believe may hold similar reserves to those found in West Africa .

The deal, to take 40% stakes in concessions in the Barreirinhas and Ceara basins held by state-owned energy giant Petroleo Brasileiro SA (PETR4.BR), or Petrobras, also signals BP's latest foray into one of the world's most promising oil and gas frontiers.

Financial terms of the transaction weren't disclosed, but a BP spokesman said it involved the
U.K. company "meeting certain past and future exploration costs."

Bountiful hydrocarbon discoveries in the last decade have led to a near 70% rise in the South American country's proven oil and gas reserves, where 11 of the 35 biggest worldwide finds have occurred.

Much of that success has been achieved by tapping reservoirs contained beneath an ultra-deep layer of salt that lies thousands of meters below the seabed.

BP last year paid $3.2 billion to buy nine exploration licenses from Devon Energy Corp., giving the energy giant access to the
Campos Basin , one of the areas where these "presalt" crude deposits are found.

By contrast, BP's latest acquisition is in a frontier exploration area known as the equatorial margin. The geology is mirrored on the opposite side of the Atlantic, once part of the same land mass, and many oil producers hope that the waters off the coast of northeastern Brazil, French Guiana, Suriname and Guyana hold similar deposits to those discovered off West Africa, like Tullow Oil PLC (TLW.LN) and Apache Corp.'s (APC) giant Jubilee find.

These hopes were confirmed last September when Tullow, Royal Dutch Shell PLC (RDSB) and Total SA (TOT) consortium made a large discover off the coast of
French Guiana .

"These four new blocks bring exciting new exploration opportunities, adding to the already significant position we hold in
Brazil ," said BP Chief Executive Bob Dudley.

BP will now hold some equity in some 14 oil and gas fields in
Brazil , with operational control over six of them.

Petrobras will partner the
U.K. firm in nine of the concession areas.