The Alberta government launched a long-range campaign last week to make oil and gas companies pay for cleaning up a generations-old and growing backlog of 96,969 depleted and inactive wells.

Energy Minister Sonya Savage announced a stiffened polluter-pay policy that requires producers to devise five-year cleanup plans and act on them under supervision by the Alberta Energy Regulator (AER).

The policy grants landowners the right to nominate discarded wells on their property for prompt cleanups. Oil and gas firms would have to justify postponing action on the requests.

The cleanup backlog includes 21% of 456,729 Alberta wells licensed since 1914 that grew through an environmental loophole. Producers have been able to cap depleted bores, instead of permanently plugging and...