MONTREAL -- Canada needs a stepped-up infusion of public and private investment to help its economy overcome the punishing impact of low oil prices, which won't enjoy a big rebound amid global uncertainty, the head of the Caisse de depot said Wednesday.

The high level of uncertainty is caused by several factors, including the return of Iran to oil markets, reaction to the rise of U.S. shale, output decisions by Saudi Arabia and oil production in Russia -- all of which make it difficult to predict future prices.

"It's probably likely that we're getting closer to a floor on oil prices, but where is that floor and when will we find it and when will we begin to see a step-by-step improvement in the price of oil -- that's not clear," CEO Michael Sabia said after releasing the pension fund manager's 2015 results.

He said Quebec's largest pension fund manager is open to investing more in Bombardier, although it has no immediate plans to do so after spending US$1.5 billion for a 30-per-cent stake in the transportation company's railway division.

"We have an important investment in a subsidiary of Bombardier. For now, that represents significant exposure," he said, adding he supports government investment in Bombardier's CSeries commercial aircraft as a way to reduce the company's risk.

"If those risks get reduced I think you'll probably see some change in the valuation of the company so I think that's the catalyst. It's a risk-reduction story."

Sabia expects global financial volatility will continue over the next few years as countries adjust to the withdrawal of monetary stimulus and anemic global growth.

"The party's probably over in terms of double digit returns that we've all gotten very comfortable with over the last number of years."

Despite market volatility, the Caisse generated a 9.1 per cent return on investments last year as its net assets grew to $248 billion, mainly due to a $20.1-billion increase in net investments.

The gains last year were smaller than the 12 per cent earned in 2014, but it beat the 6.7 per cent growth in the reference index of returns by private and public institutions.

Although it can't be immunized from market downturns, Sabia said the Caisse has repositioned itself and changed the way it invests to cushion any blows.

He wouldn't predict if high single-digit returns are sustainable, but said it aims to generate six to 6.5 per cent annual return over the long term to meet the needs of depositors.

Faced with uncertain public markets and lower forecasted fixed income returns, the Caisse plans to further expand its global portfolio.

For the first time in its history, a majority of its investment exposure is located outside Canada, rising to 54 per cent from 41 per cent in 2011.

The United States was the biggest foreign market, accounting for 26.6 per cent of the Caisse's $75.6 billion overall global investment. Some 40 per cent of its $55-billion real-estate portfolio is now across the border.

Assets in Quebec totalled $59.7 billion, a slight dip from 2014 because of the sale of its investment in Valeant Pharmaceuticals.