The Alberta Energy Regulator says excessive steaming was one of the reasons behind high-profile leaks at Canadian Natural Resources Ltd.'s Primrose oilsands project nearly three years ago.

The watchdog's final report on the incident cites the ability of the bitumen-water mixture to make its way to the surface through old well bores and natural and man-made fractures in the rock.

CNRL had been using an extraction technique at the eastern Alberta project called high-pressure cyclic steam stimulation, the safety of which has been questioned by environmental groups.

Roughly 1.2 million litres of the bitumen-water emulsion were recovered and 20.7 hectares were affected at CNRL's Primrose East, located 250 kilometres northeast of Edmonton.

AER executive vice-president Kirk Bailey says high-pressure cyclic steam stimulation has a good track record elsewhere in the province and there are currently no concerns about its use by other operators.

The AER says CNRL didn't break any rules with its steaming technique, but the regulator has ordered the company to permanently reduce its steaming volumes at the site to make sure a similar incident doesn't happen again.

The pressure restrictions may affect the pace at which CNRL is able to produce bitumen at Primrose.