SEOUL, April 30 (Reuters) - SK Innovation Co Ltd

, owner of South Korea's biggest oil refiner SK

Energy, swung to an unexpected operating loss in the first

quarter, but forecast refining margins would gradually recover

this quarter amid higher driving season consumption.

The company posted an operating loss of 45 billion won ($32

million) for January-March, versus a 625 billion won profit a

year earlier. That compared with analysts' average forecast for

a 393-billion-won profit, according to LSEG SmartEstimate.

The firm sank to loss as profits declined quarter-on-quarter

at its refining, oil exploration and production, and lubricants

businesses. Losses also deepened at its petrochemical business

and persisted at its battery business as the global economic

slowdown continued, the company's earnings presentation showed.

First-quarter revenue rose 12.2% to 21.1 trillion won.

Shares in SK Innovation closed down 2.5% before the earnings

announcement, versus the benchmark KOSPI's 0.3% fall.

($1 = 1,420.6900 won)