SINGAPORE, April 20 (Reuters) - Taiwan's Formosa Petrochemical Corp plans to ramp up operating rates at its refinery in May to 74% once it restarts a gasoline-making unit after maintenance and as refining margins have improved, the company's spokesman said.

Formosa plans to process 400,000 barrels per day of crude in May, or 74% of its total capacity, up from 340,000 bpd in March and April, spokesman KY Lin told Reuters.

(Reporting by Florence Tan; Editing by Tom Hogue)