The Alberta government's earnings from the sale of leases for petroleum rights have shrunk by about $230 million this year, according to the National Energy Board.

So far in 2015, the province has collected $263 million. Last year it took in $494 million, the national regulator said in a release Thursday.

Both totals are a far cry from 2011, when the province earned a record $3.6 billion.

"It's a predictor of future activity," said Winston Gaskin, head of Vertex Professional Services.

He says over his 21-year career helping companies buy land rights, he has never seen a downturn like this one.

"The land sales are telling us the investment dollars are not there, companies are not spending, and they're not planning activity levels that are significant over the course of the next three to five years."

The NDP government says it is factoring the lower land sales into its budget, along with the drop in resource royalties.

The NEB says oil and gas land revenue is poised to be the lowest in decades across Western Canada:

Saskatchewan: land sale revenues totalled $45.5 million in the first 10 months of 2015, compared to $197.9 million over the same period last year. The province earned a record $1.1 billion in 2008.

British Columbia: land sale revenues totalled $12.3 million so far in 2015, compared to $383 million in all of 2014. The province earned a record $2.7 billion in 2008.

Manitoba: revenues in 2014 and so far in 2015 are about $1.5 million each. They peaked in 2010 at $13 million.