South Korea’s third-largest oil refiner S-Oil on Sunday finished the four-day cleanup work for the spill that occurred at a storage tank in Ulsan.

About 138,000 barrels, or 21.9 million liters, of crude oil spewed from the tank since Friday after a mixer within the facility went off course, S-Oil officials said in a statement. Three-meter-deep concrete dikes surrounding the tank prevented the oil from flowing into the sea.

As of Sunday afternoon, 381,000 barrels of crude oil remaining in the tank has been transferred to a nearby storage facility, according to the firm. The spilt oil will be retrieved within two or three days, the officials added.

“All S-Oil employees are focusing on preventing a further damage in the cleanup work,” S-Oil CEO Nasser Al-Mahasher said at a press conference at the Ulsan plant on Sunday.

“We’ve extended their cleanup efforts, such as setting up oil fences and oil-absorbent pads, to prevent possible sea pollution,” the CEO added.

The spillage began at around 3:30 p.m. on Friday when the tank carrying 570,000 barrels of crude was damaged due to a broken mixer.

Korea has experienced a number of major oil spills in recent years, with the 2007 spillage off the coast of Taean, South Chungcheong Province, being the worst in its history. More than 12,000 tons of crude oil were dumped into the West Sea after a tanker’s hull was pierced in a crash.

The latest spillage occurred in Yeosu, South Jeolla Province, in February 2014, after a Singapore-registered oil tanker collided with oil pipelines.

By Suk Gee-hyun (monicasuk@heraldcorp.com)