South Korea's March imports from Iran more than doubled from a year ago to a record of 18.54 million barrels, or 597,935 barrels per day (bpd), data from state-run Korea National Oil Corp (KNOC) showed on Monday, Reuters reported.
For the January-March period of 2017, Iran seized the No.2 spot with shipments of 46.73 million barrels, also more than double from the same period last year and the highest on record for a quarter.
In the first quarter of 2016, Iran was South Korea's fifth-biggest oil supplier behind Saudi Arabia, Iraq, Kuwait and Qatar, according to KNOC data.
This year's surge in Iranian crude supply came after Tehran was exempted from production cuts led by the Organization of the Petroleum Exporting Countries (OPEC) to clear a global glut.
Iran's jump to the No.2 spot is also due to solid condensate demand from South Korean refiners such as SK Energy and Hyundai Oilbank.
Saudi Arabia held onto its spot as South Korea's top oil supplier for both March and the full quarter.