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Oil major Exxon Mobil Corp is scheduled to shut down its Jurong Island refinery in Singapore, the smaller of its two facilities in the city state, for a month from May next year.

The routine maintenance shutdown of the 296,000 barrels-per-day facility will last from early May to early June and includes taking down in stages both the plant's crude distillation units (CDUs), according to industry sources.

The Jurong Island facility operates two crude distillation units (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.

Industry sources said some other secondary units at the plant, which produce mainly middle distillates such as gas oil and jet fuel, will also be taken down in stages.

Traders said the shutdown is unlikely to have a major impact on the products market as planning is being carried out long in advance and the country's other refinery will also be running.

In addition, the middle distillates market has been weak since the beginning of the year and has seen refineries around the world running at reduced rates of between 70-85 percent. The three refiners in Singapore - ExxonMobil, Shell and Singapore Refining Co - have been running at 80-85 percent capacity, compared to more than 90 percent when the market was healthier.

Together with Exxon's 309,000-bpd refinery on mainland Singapore, the facility is the world's fifth largest such complex.

Earlier this year, the U.S oil major carried out maintenance at both its mainland and Jurong Island refineries between February and the end of April.

Visbreaking units at both plants were shut in stages, which in turn had an impact on the production of fuel oil between early-March and April. It led to the company running short of fuel oil to sell to the Singapore fuel oil cargo market and supplies to the Hong Kong bunker market were also said to have decreased as a consequence.

ExxonMobil's fuel oil supplies from its mainland refinery are drawn from its three visbreaking units, which crack residues left over from the crude distillation units into higher-value products.

When monthly production is running normally at around 600,000-650,000 tonnes, Exxon reportedly sells around 50 percent to the Singapore bunker market and 40,000-80,000 tonnes to the Singapore cargo market. Approximately 200,000-250,000 tonnes are also sent to Hong Kong.

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