UPDATE 1-S.Korea refiners to export 1.2 mln bbls diesel in Sept

* SK Energy, GS Caltex to export 600,000 bbls each in Sept

* Hyundai Oilbank to skip Sept spot diesel exports

SEOUL, Aug 10 (Reuters) - Major South Korean refiners SK Energy (096770.KS) and GS Caltex will export 600,000 barrels of spot diesel each in September, while smaller Hyundai Oilbank Corp will skip exports, company sources said on Monday.

The country's top refiner SK Energy, which has a crude refining capacity of over 1.1 million barrels per day (bpd), will maintain September spot diesel exports at 600,000 barrels, steady from August but lower than July's 900,000 barrels.[ID:nSEO233076]

"Refining margins are not yet good enough for us to raise exports," a company source said. SK Energy will also shut down its No.4 crude unit with a refining capacity of 240,000 bpd for maintenance in September. [ID:nSEO369842]

Profit margins for complex refiners in Asia processing Dubai crude stood at $2.39 a barrel, improving from minus $0.05 in July due to weaker run rates but still below $2.89 in January. [REF/MARGIN1]

A source at the country's No.2 refiner GS Caltex also said it would export 600,000 barrels of spot diesel in September, swinging back to July export levels after exporting zero in August as refining margins had improved. [ID:nSEO232594]

Singapore gas oil crack spread stayed above $8.00 a barrel on Friday, helped by refinery run cuts in Europe. <ASIA/SWAP/FUEL>

But traders said there had been no improvement to fundamentals, which have been weak since the first quarter, as demand to pull Asian barrels to Europe eases due to a narrowing contango and with volumes on floating storages already at over 70 million barrels.

A company source at Hyundai Oilbank said that it would skip spot diesel exports next month after exporting 400,000 barrels in August due toto lower runs on its delayed coking unit (DCU). [ID:nSEO52441]

"We have slashed the DCU's operation rates to 60 percent from the usual 100 percent since end-July due to poor margins, affecting diesel production the most," the source said.

Hyundai Oilbank's 35,000-bpd capacity DCU converts low value residual oil products to lighter products of higher value.

(Reporting by Cho Meeyoung; Editing by Jonathan Hopfner)