Oil is unlikely to return to $80 a barrel before the end of the next decade, despite unprecedented declines in investment, as yearly demand growth struggles to top 1 million barrels per day, the International Energy Agency said on Tuesday. In its World Energy Outlook, the IEA said it anticipates demand growth under its central scenario will rise annually by some 900,000 barrels per day to 2020, gradually reaching demand of 103.5 million bpd by 2040.