Tesoro Corp. has told state officials that it expects to lay off 210 workers in May when it shuts down its refinery in Kapolei, more than the 180 to 200 employees  previously estimated  by the company.

Tesoro announced on Jan. 8 that it planned to close the refinery and  convert it into an import, storage and distribution terminal.

The updated layoff count was included in a letter Tesoro sent Feb. 28 to the state Department of Labor and Industrial Relations. Federal law requires employers to provide notice at least 60 days in advance of any mass layoffs of 100 workers or more.

“Approximately 210 employees will be separated from employment. At this time the company anticipates that a group of affected employees will be terminated sometime during a 14-day period beginning on May 1, 2013,” according to the notification letter written by Thomas Weber, vice president of Tesoro’s Kapolei refinery.

“This announcement and the above timetable are based on the best information currently available,” Weber wrote. “however, various factors may still affect these plans and the timing of employee separations.”

Tesoro is seeking a buyer for the terminal, as well as its local network of 31 gas stations.

San Antonio-based Tesoro put the underperforming refinery up for sale in January 2012, but was not able to find a buyer.

The Tesoro plant is the state’s largest of two refineries with a capacity of 94,000 barrels a day. It employs 240 people. The other refinery, operated by Chevron, has a capacity of 54,000 barrels a day.