UPDATE 3-S.Korea's Aug crude oil imports down 3.8 pct yr/yr -KNOC

* Aug crude imports at 72.8 mln bbls vs 75.6 mln bbls yr ago

* Crude runs at 74.8 mln bbls, down 1.1 pct y/y

* Domestic oil product demand up; exports surge y/y

* End-Aug private oil stocks at 62.6 mln bbls, up 4.7 pct y/y (Updates graphic)

By Cho Mee-young

SEOUL, Sept 22 (Reuters) - South Korea's crude oil imports fell about 4 percent on the year in August, swinging from two months of year-on-year growth due to delayed maintenance shutdowns at some local refining units.

Crude imports by South Korea, the world's fifth-largest crude buyer, stood at 72.8 million barrels last month compared to 75.6 million barrels imported a year earlier, state-run Korea National Oil Corp (KNOC) said on Thursday.

The economy ministry, citing tentative customs figures, said earlier this month that the country's crude oil imports last month dropped 3.6 percent to 72.9 mln barrels from a year earlier.

South Korea's third-largest refiner S-Oil shut down a 240,000-barrel-per-day (bpd) crude distillation unit (CDU) from Aug. 7 through the end of the month for planned maintenance that was delayed from May.

Analysts said crude imports in September and October are projected to remain bearish year-on-year also because of maintenance shutdowns at some CDUs of the country's top refiner SK Energy and second-largest GS Caltex.

They also said that the global economic slowdown had weighed on South Korea's crude demand, and refiners had tried to reduce inventory costs by lowering imports.

"Refiners seemed to slash their crude inventory to save costs, while actively shipping out their oil products," Kim Jae-joong, senior analyst at Woori Investment & Securities, said.

Brent crude LCOc1 hit a peak just above $127 a barrel in April, and at current levels below $110 a barrel, it is still about 15 percent higher than at the end of 2010. In August, Brent dipped to below $100 a barrel.

EASING CRUDE RUNS; EXPORTS SURGE

The country's crude runs eased by 1.1 percent year-on-year in August to 74.8 million barrels, with refinery profit margins marking a year high of $4.96 a barrel in August before easing to $4.20 a barrel on average in the last 15 days.

Oil product exports jumped 13 percent in August on the year to 35.1 million barrels, according to KNOC data.

Of the total exports in August, gasoline accounted for 4.9 million barrels, up 41 from a year earlier, while diesel exports rose by 15 percent to 13 million barrels.

The country's private oil inventories by the end of August stood at 62.6 million barrels, up 4.7 percent from 59.8 million barrels a year earlier but down 6.4 percent month on month, the data showed.

Domestic demand for oil products last month was at 67.3 million barrels, up 1.8 percent year on year.

High oil prices have been limiting demand growth in South Korea, which is battling to trim inflation led by costlier energy and commodities. (Additional reporting by Seongbin Kang; Editing by Jonathan Hopfner and Miral Fahmy)