The rise in the crude oil imports along with higher crude run rates was due to healthy refining margins, industry experts said. Refinery profit margins have jumped to $3.34 on average in March, $2.75 in February and $1.21 in January.

Buoyed by strong margins, four local refiners -- SK Energy, GS Caltex, S-Oil and Hyundai Oilbank -- and state-run KNOC imported a combined 80.1 million barrels last month, compared with 66.8 million barrels a year earlier, according to data posted on KNOC's web site.

The country's crude oil imports are likely to stay at such high levels also in April as SK Innovation , which owns South Korea's top oil refiner SK Energy, purchased 2 million barrels from quake-hit Japan for early April arrival as they announced last month.

Under a swap deal, SK Innovation will also receive another 2 million barrels of crude oil for late April shipment from the Middle East instead of Japan, where an earthquake and tsunami crippled some refiners.

In March, South Korea's crude runs increased 15.1 percent year-on-year to 78.4 million barrels, while domestic oil product demand rose 3.2 percent year-on-year to 68.8 million barrels in February, the data showed.