Aug 12 (Reuters) - The discount on Western Canada Select

(WCS) heavy crude versus the North American benchmark West Texas

Intermediate (WTI) narrowed slightly on Monday:

* WCS for September delivery in Hardisty, Alberta, settled

at $12.80 a barrel below WTI, according to brokerage CalRock,

having settled at $13.20 a barrel under the U.S. benchmark on

Friday.

* Canadian heavy crude differentials have gained support

this month from some U.S. Midwest refineries restarted

operations after unplanned shut-downs in July.

* Exxon Mobil ( XOM ) restarted select units at its 251,800

barrel-per-day refinery in Joliet, Illinois, three weeks after

it lost power following a storm, the company said last week.

* However, Exxon reported a unit upset at Joliet on Saturday

and Sunday, according to Illinois Emergency Management Agency

* Imperial Oil ( IMO ) said its Sarnia site reported the

beginning of maintenance work on process equipment, according to

a community alert

* Global oil price jumped by more than 3%, rising for a

fifth consecutive session on expectations of a widening Middle

Eastern conflict that could tighten global crude oil supplies