Standard and Poor's has downgraded Alberta's credit rating, citing concerns with the province's weak revenue forecasts in the next two years and its growing debt burden.

The ratings agency dropped the province's credit one notch to AA+, down from its previous level of AAA.

Finance Minister Joe Ceci said he was "disappointed" by the downgrade, blaming it mainly on the low price of oil.

"This downgrade is a result of the over-reliance of non-renewable resource revenues in our budget," Ceci said.

"That's why we're taking steps to diversify our economy," he added.

​Ceci said he doesn't expect the change to affect borrowing costs because he believes Alberta's investors have already recognized the impact of low oil prices on provincial finances.

"The markets have already reacted to this reality, so we don't anticipate that it's going to have much impact at all," the finance minister said.

Ceci also said the province has no plans to slow borrowing-intensive capital spending in response to the downgrade — quite the opposite, in fact.

"Investing in capital infrastructure development throughout the province will have a positive impact on our GDP," he said.

Wildrose says they predicted this

Opposition Wildrose Leader Brian Jean and finance critic Derek Fildebrandt released a joint statement about the downgrade, which they blamed on provincial spending.

"Wildrose had warned the NDP that without any serious plan to get a hold of government spending, Alberta would see a credit downgrade," they wrote in an email.

"This should be a wake-up call for the NDP that we can no longer afford to maintain the most expensive and wasteful government in Canada."

Standard & Poor's explanation

The ratings agency cited Alberta's "oil price-driven" budget and "now-average economic prospects" in explaining the rationale for its decision.

Overall, however, it noted it still considers the province to be among the most reliable of borrowers.

"The ratings reflect Standard & Poor's view of Alberta's exceptional liquidity, very strong financial management, still strong economy and budgetary flexibility, and low contingent liabilities," the agency stated.

"We assess the provincial economy as strong despite the plunge in oil prices and declining real GDP that we expect for 2015," it added.