Aug 14 (Reuters) - The discount on Western Canada Select

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

Intermediate (WTI) narrowed on Wednesday, for the fourth

straight day:

* WCS for September delivery in Hardisty, Alberta, settled

at $12.40 a barrel below WTI, according to brokerage CalRock,

having settled at $12.60 a barrel under the U.S. benchmark on

Tuesday, for the fourth trading session in a row

* 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

* Global oil prices settled 1% lower on Wednesday after U.S.

crude inventories rose unexpectedly and as worries eased

slightly that a wider Middle East conflict could threaten

supplies from one of the world's major regions for crude

production.