UPDATE 1-Petrobras confirms new subsalt light oil find

(Recasts, adds details on well, Sugar Loaf structure)

RIO DE JANEIRO, May 21 (Reuters) - Brazil's state-run oil company Petrobras (PETR4.SA)(PBR.N) said on Wednesday a formation test on a well at the BMS-8 block confirmed the presence of light oil in a new promising subsalt cluster find.

The offshore BMS-8 block in the Santos basin is operated by Petrobras, while Royal Dutch Shell (RDSa.L) and Portugal's Galp (GALP.LS) have stakes of 20 percent and 14 percent respectively.

Petrobras provided no reserve estimates or clues on whether recent subsalt discoveries in the area are part of a single oil-bearing structure.

Many analysts believe the block's oil accumulation is part of a larger structure, known as Sugar Loaf/Carioca.

Last month, the head of Brazil's ANP oil market regulator, Haroldo Lima, announced a reserve estimate for the structure at 33 billion barrels. However, he later said the estimate had been made by analysts.

The pioneer well at the BMS-8 is located around 250 km from the Sao Paulo state coast, at a water depth of 2,139 meters with total drilled depth of 6,773 meters, Petrobras said. Oil accumulations were found at a depth of around 6,000 meters. The crude is between 25 and 28 API grade.

The consortium is preparing an evaluation plan for the find to be submitted to Brazil's National Petroleum Agency (ANP).

The Sugar Loaf structure lies close to the Tupi field, where Petrobras last year made a recoverable reserve estimate of between 5 billion and 8 billion barrels, making it one of the biggest oil discoveries in the past 20 years.

Other companies involved in Sugar Loaf blocks include U.S. firms Exxon Mobil Corp (XOM.N) and Hess Corp (HES.N) and Britain's BG Group Plc (BG.L).

Petrobras has said more drilling was needed in the area to establish the reservoir volumes. It has said it expects more precise data by July.

Analysts are bullish on Brazil's oil potential, expecting the country to become a major world oil producer with big reserves of light oil in the subsalt cluster.

Stocks in Galp and Shell rallied 5 percent and 4.72 percent, respectively, earlier on Wednesday on expectations of the find announcement. Petrobras shares rose 1.65 percent even as the broader market in Brazil fell. (Reporting by Andrei Khalip; Editing by Christian Wiessner)