The world's fifth-largest crude importer won a six-month sanctions waiver from Washington in November, allowing it to purchase a limited amount of oil from Iran, but has been working to overcome payment and insurance issues.

South Korean buyers can buy up to 200,000 barrels per day of Iranian oil under the waiver, mainly condensate, according to industry sources, and oil imports from Iran are expected to resume this month, a source has told Reuters.

One South Korean buyer was set to receive nearly 2 million barrels of Iranian condensate in January, with the first condensate cargo of about 960,000 barrels set to arrive this week, the source said.

For 2018, South Korea's imports of Iranian oil fell to 7.15 million tonnes, according to customs data. In 2017, South Korea bought 18.07 million tonnes, making Iran its No.3 crude supplier.

In total, South Korea imported 12.38 million tonnes of crude oil in December, down 6.6 percent from 13.25 million tonnes from a year earlier.

For the year, the country imported 148.60 million tonnes of crude, down 0.1 percent from 148.68 million tonnes in 2017, the data showed.

Saudi Arabia remained the top oil supplier, delivering 43.60 million tonnes of crude in 2018, up 1.3 percent from 43.06 million tonnes last year, according to the data.

In the absence of Iran oil, oil shipments from the United States more than quadrupled to 7.87 million tonnes in 2018, reaching an all-time high.

Final crude imports data from state-run Korea National Oil Corp (KNOC) is set to be released later this month.

(Reporting By Jane Chung; editing by Richard Pullin)

By Jane Chung