(CNBC) Oil prices pared some of their losses on Wednesday after falling to near seven-year lows earlier in the week, but those hoping for a rebound next year may be disappointed.

Fatih Birol, the executive director of the International Energy Agency (IEA), told CNBC that crude prices could continue to fall in 2016, presenting a challenge to governments that are trying to encourage the use of relatively expensive sustainable energy.

“When we look at 2016, I don’t see many reasons why we can see upward pressure on the prices… Demand is weaker and we may well see Iran come back (to the market) and there will be a lot of oil,” Birol said, talking from the sidelines of the COP21 climate conference in Paris.

“So 2016 may well be another year with lower prices and this will have implications of course for investments in the oil sector.”

Brent and West Texas Intermediate (WTI) crude oil prices fell below $40 per barrel this week for the first time since early 2009. Both types of oil rallied on Wednesday, but WTI prices remained below $40, trading at just over $38. Brent traded at around $40.75 per barrel.

Oil prices have tumbled since June last year due to supply and demand imbalances. U.S. shale gas production has risen and OPEC has maintained output, while demand from China, a massive consumer of commodities, has waned.