Brazil seeks large share in big oil fields-report

(Adds details on new drilling plans, paragraphs 8, 9)

SAO PAULO, Aug 7 (Reuters) - Brazil is considering changes
to oil legislation that would secure the government large
stakes in the biggest fields in the massive sub-salt oil region
off the nation's coast, Chief of Staff Dilma Rousseff told
Valor Economico in an interview published on Friday.

In 2007 Brazil discovered some 8 billion barrels of crude
in the Tupi field, opening a new oil exploration frontier deep
below the Atlantic that could hold more than 50 billion
barrels.

The government is drafting new oil laws to boost state
control over the massive finds, including proposals for the
state to impose limits over private companies' participation on
the exploration and commercialization of that oil.

The government will decide on a case-by-case basis the
percentage of production it wants from each sub-salt field that
could be put up for auction, Rousseff told Valor.

In the most productive fields the government may hire
state-controlled oil company Petrobras (PETR4.SA) as its sole
operator, Rousseff said.

"In fields we are certain of the existence of big reserves,
we will hire Petrobras directly. In that case, we won't hold an
auction," she said.

Petrobras' share in the blocs will be defined by law,
Rousseff said, without elaborating. The Brazilian government's
share in the fields will, therefore, be allowed to fluctuate
partly to open space for private oil companies if necessary,
Valor reported.

Brazil's state energy regulator ANP on Friday told
Petrobras it was interested in hiring the company to evaluate
the potential reserves of sub-salt blocks that have not yet
been auctioned, according to an ANP official.

The ANP usually carries out seismic studies to compile
geological data used for bidding rounds. This would be the
first time the regulatory agency hired Petrobras.

President Luiz Inacio Lula da Silva has yet to sent new oil
legislation to Congress and is still debating with advisors
what measures to include. The changes are expected to face
stiff resistance from Congress and Energy Minister Edison Lobao
this week said even cabinet members had important
disagreements.
(Reporting by Guillermo Parra-Bernal, Brian Ellsworth and
Denise Luna; Editing by David Gregorio)