As we've covered extensively in the past (here and here), home prices and vacant offices in Calgary have been a complete disaster as a result of the collapse in oil prices. Recall the troubling divergence in home prices that Calgary is experiencing in relation to other major cities in Canada.

And also, vacancy rates ebb and flow with the price of crude.

And now with the price of crude hovering around $40/bbl, CBRE Canada estimates that Calgary's downtown office vacancy rate was 20.2% as of March 31, nearly twice as high as the 11.8% a year ago. This means that one in five offices is now vacant.

It says vacancies are at historic highs, with eight million of the downtown area's 41 million square feet of office space available and subleases making up close to half of what's on offer

With three million square feet of office space under construction still, experts say that it could be well over a decade before the market rebalances.

Calgary’s downtown commercial office space vacancy rate has

risen to 20.2%, according to CBRE.

As CTV News adds, "it's the first time since 1983 that more than one fifth of office space was available in downtown Calgary, and the city is on track to hit a new record above the 22 per cent rate hit that year", citing Greg Kwong, regional managing director at CBRE.

"It's going to get a little bit worse before it gets better," said Kwong. "Unless oil jumps back to $80 a barrel, I don't think we'll go down to the teens."

Or, we may, if oil goes back to $30 or lower.

How bad is the damage: "prices have dropped to an average of $20.97 per square foot for high-end class A office space from $29.23 in the same quarter a year ago, CBRE added."

The dramatic reversal in the local markets, duly reported here for the past year, has caught Kwong by surprise, and he is stunned at how quickly Calgary's market has reversed from the 2009-2014 trend, when it had the lowest vacancies and highest rental rates in Canada.

"It was amazing how robust the market was in November 2014, and literally within four or five months it was amazing how ugly it got here," said Kwong.

Alas, that's what happens when the one commodity that powers the city's economy has its price cut by 60%.

Meanwhile, Calgary's office market has been hit hard as oil and gas companies continue to cut jobs and consolidate office space due to low crude prices. Barclay Street Real Estate released a report Tuesday saying MEG Energy is trying to sublease more than 300,000 square feet, Shell Canada more than 183,000 square feet and Penn West Energy 73,000 square feet.

And once the bankruptcies begin in earnest, it will only get worse.

For now Calgary largely an outlier in Canada's downtown office market, with Toronto's vacancies up only slightly in the quarter to 5.3%, while Vancouver's dropped to 8.8%, according to CBRE. However, we all know the "Vancouver story" by now.

Ultimately the real number is even worse as vacancy rates also don't account for the unknown amount of near-empty office space that companies haven't tried to sublease because there's no market for them, said Kwong. "You'll see some buildings where there are five people on a 40,000-square foot floor," he said.

But not for long. As for the immediate future, things are only set to get worse:

Dan Lannon, a senior vice-president at real estate company Colliers International, said with about three million square feet of office space under construction, the downtown core could have 11 million square feet of empty offices in 2018. That's the equivalent of about 647 NHL rinks. "The fact is we're adding a lot of office space to our market that our city really doesn't need," said Lannon.

With Calgary absorbing an average of about 550,000 square feet of office space per year over the past 15 years, Lannon said it "could be well over a decade before the city returns to a balanced market."

And that assumes oil returns to its historic prices.