CALGARY, Alberta—Three large Canadian oil spills over the past 30 days have increased concern over pipeline safety here, just as the government and the Canadian petroleum industry are trying to drum up support for a series of new pipeline projects.

Enbridge Inc. said late Tuesday that one of its pipelines, carrying heavy oil-sands crude, spilled some 1,450 barrels in eastern Alberta earlier in the week. Earlier this month, Plains All American Pipeline LP spilled up to 3,000 barrels into a reservoir near the small resort town...