* Output falls from Petrobras, Shell, Statoil-run fields
* BG Group surpasses Statoil to become No. 2 producer
RIO DE JANEIRO May 3 (Reuters) - Brazil's output of oil and natural gas fell in March to its lowest level in more than 3-1/2 years, as three of the biggest producers closed offshore oil platforms for repairs, the country's oil regulator said on Friday.
Brazil produced an average of 2.339 million barrels of oil and natural gas equivalent per day (boepd) in March, the lowest monthly average since August 2009, the regulator, known as the ANP, said in a statement. Output slid 6.6 percent from a year earlier and 6.4 percent from February.
The bulk of the decline came after Brazil's state-controlled Petroleo Brasileiro SA,, or Petrobras, shut its P-54 platform in the giant Roncador field, Brazil's No. 2 producing area.
Royal Dutch Shell Plc, shut the FPSO Espirito Santo platform, which it operates with partners Petrobras and India's ONGC Ltd. Norway's Statoil performed maintenance on the Maersk Peregrino platform, which it operates with China's Sinochem.
The declines would have been larger were it not for record natural gas output of 77.3 million cubic meters a day, or 486,000 boepd. Crude oil output of 1.853 million barrels per day (bpd) was the lowest since December 2008 and only the second result in more than two years below 2 million bpd.
With March's decline, Brazilian oil and gas output has posted 24 straight months of declines from the year earlier period.
Petrobras, responsible for 93 percent of Brazilian output, faces falling output from aging fields, delays in development of giant new offshore reserves and continuing maintenance in some of the company's oldest and most-productive offshore areas.
Petrobras output will increase in the second half of 2013 as new platforms come online and some maintenance winds down at existing production sites, Jose Formigli, the company's production chief said on Monday.
Rio de Janeiro-based Petrobras remained the No. 1 producer with average daily ownership of 2.174 million boepd of oil and gas output in March. The figure reflects Petrobras' share, or ownership, of output from fields in which it owns a stake.
BG Group Plc overtook Statoil in second place with 38,779 boepd. Thanks to maintenance in the Peregrino field in the Campos Basin, Statoil slipped to 13th place and its partner Sinochem dropped to 16th from fifth according to the ANP.
Brazil's QGEP Participacoes SA, moved into third spot with 18,919 boepd. Shell slipped to fourth place with 17,847 boepd.
OGX Petroleo e Gas SA, operated by Brazilian billionaire Eike Batista, saw its offshore operations slip again, dropping 26 percent in the Tubarao Azul field to 8,282 barrels a day. The oil company ranked ninth in output, the same as February, when it produced 11,318 boepd.
OGX Maranhao, Batista's on-shore gas company, saw output rise 24 percent to 10,262 boepd. It rose to No. 7 in the ranking.
Taken together the two OGX companies' output surpasses Shell's. Their production would be enough to ranked fourth if the ANP did not count the two units output separately.