* WCS quoted at $17.75-$18/bbl under WTI
* Keystone to be restricted 20 percent in Aug
* Synthetic $9.45/bbl over WTI
CALGARY, Alberta, July 15 (Reuters) - Canadian heavy crude prices gained strength on Friday as steady demand overshadowed word that flows on TransCanada Corp's (TRP.TO) Keystone pipeline will be restricted again next month.
Western Canada Select heavy blend for August delivery was discussed at $17.75-$18 a barrel under benchmark West Texas Intermediate crude, compared with $18-$19 earlier this week.
TransCanada said it is restricting volumes on its Keystone pipeline system by 20 percent next month, although trade sources pointed out that the system normally runs below capacity. [ID:nN1E76E0F5]
Heavy spreads have narrowed by as much as $5 a barrel in the past two weeks as some refineries wrapped up maintenance, and stored volumes at the Hardisty, Alberta, storage and pipeline hub have drained off.
According to Genscape, Hardisty inventories are down 25 percent to 7.7 million barrels in the past four weeks.
September WCS, meanwhile, was discussed at $20.50 under WTI.
Light synthetic crude for August was quoted at above $9.45 a barrel over WTI, about 20 cents richer than levels earlier this week.
The crude, derived from the Alberta oil sands, has held reasonably steady after Suncor Energy Inc (SU.TO) completed more than six weeks of planned maintenance on its Upgrader 2 last month. (Reporting by Jeffrey Jones; editing by Peter Galloway)