July 17 (Reuters) - Exxon Mobil's ( XOM )

251,800-barrel-per-day refinery in Joliet, Illinois, is likely

to have most units offline through this week, industry monitor

IIR said on Wednesday.

A severe storm passed through Joliet earlier this week,

leaving thousands without power.

The power outage took 16 units offline on Monday night,

according to data from IIR.

Among them are a 127,000-barrels-per-calendar-day (bcd)

vacuum distillation unit and a 98,000-bcd fluid catalytic

cracker unit. Four hydrotreater units and three sulfur recovery

units also went down during the outage.

The units are expected to be down for a week with plans to

restart over the upcoming weekend, according to IIR.

Exxon did not immediately respond to a request for comment.

The outage sparked panic buying in the Chicago wholesale

market, pushing prices higher for refined products in the

region. Chicago diesel traded at a discount of 2.50 cents

against the ultra-low sulfur diesel futures benchmark on

Wednesday, 15.25 cents higher than Tuesday.