Canada's Suncor Energy on Wednesday said it is weighing options for replacing around 200 000 bbl/d of raw bitumen supply from its largest oil sands mine, which is set to run out by the mid-2030s.

Base Mine, situated just north of the oil sands hub of Fort McMurray, feeds two upgraders at Suncor's Base Plant in northern Alberta that produce roughly 350 000 bbl/d of high-value synthetic crude.

Suncor's plans to replace the depleting reserves ran into political hurdles last year, when the federal government warned the company that its initial proposal to extend Base Mine would not pass an environmental review because projected carbon emissions were too high.

Suncor continues to work on a regulatory application for the extension project and is also looking at other options, interim CEO Kris Smith told analysts on call to discuss earnings.

These include developing thermal oil sands projects just east of Base Plant, increasing production from its Firebag project nearby and boosting supply from its Fort Hills mine, which is linked to Base Plant via a 40 000 bbl/d pipeline.

"It's too early to call in terms of which horse is in the lead race but those options are being worked very hard," Smith said.

Last October, Suncor agreed to buy a larger stake in the Fort Hills oil sands mine from Teck Resources, which analysts said was a sign the company was looking for alternatives to extending Base Mine.

The Canadian government recently released draft guidance on requiring "best-in-class" emissions intensity for future oil and gas projects that require a federal impact assessment.

If Suncor can acquire fresh reserves to feed the upgraders from existing projects, like Fort Hills or Firebag, it could avoid an impact assessment, said Keith Stewart, senior energy strategist at Greenpeace Canada.

Smith said Suncor's focus is on keeping the upgraders full, and the choice would come down to the most economic way to do that. The company expects to land on one of the options over the next 24 months, he added.

Calgary-based Suncor reported a better-than-expected fourth-quarter profit of C$2.76-billion on Tuesday, helped by higher crude prices and tightened global supply.

The company said a decision on who will replace former CEO Mark Little would be coming very soon. Little resigned last year after a string of fatalities on Suncor sites.

The company's shares were up 1.4% at C$47.03 on the Toronto Stock Exchange.