Demand for oil in 2015 will grow far slower than previously forecast as global economies remain weak, the International Energy Agency said on Tuesday, and prices may extend their sharp fall so long as OPEC shows no sign of countering a supply surge. The IEA said it cut its 2015 estimate for oil demand growth by 300,000 barrels per day (bpd) from its previous forecast and now expects demand growth of 1.1 million bpd to 93.5 million.