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Exxon Mobil Corp is scheduled to partially close its mainland Singapore refinery and some units at its Jurong refinery for approximately one month from March for maintenance, Reuters reports.

Market sources said the visbreaking units at both refineries would be shut in stages, which would have an impact on the production of fuel oil between early-March and mid-April.

However, as the visbreaking units process residual fuels into more valuable middle distillates, the shutdown may lead to the market being flooded with fuel oil and more marine fuel being made available for the local bunker market.

ExxonMobil uses output from its 300,000 barrels-per-day (bpd) Jurong refinery - also called the Pulau Ayer Chawan (PAC)- for sale in the Singapore marine fuels market and is amongst the top suppliers at the world's largest bunker port with a market share of approximately 8 percent.

According to data released by the Maritime and Port Authority (MPA) last month, ExxonMobil was the second largest supplier in Singapore in 2008 behind BP Singapore Pte Ltd.

Traders said none of the crude distillation units (CDUs) at both refineries are expected to be closed.

The Jurong Island facility operates two CDUs with a capacity of approximately 115,000 bpd and 185,000 bpd. The smaller one was shut for over two weeks in May 2007 after a fire.

Meanwhile, the mainland refinery also has two CDUs, one with a capacity of more than 200,000 bpd and the other with up to 100,000 bpd.