The Organisation for Economic Cooperation and Development says the global economic crisis will cause unemployment to rise by up to 25 million by 2010.
OECD chief Angel Gurria said on BFM radio in France there would be "a loss of between eight and 10 million jobs in the OECD area ... and 20 to 25 million in the world as a whole" by 2010.
The International Labour Organisation earlier forecast that the number of global unemployed could go up by 20 million to 210 million people by the end of 2009.
The OECD comprises 30 countries, including all the world's industrialised economies.
Mr Gurria also said many countries would be in recession for most of 2009.
He said European countries should spend more in stimulus plans to kick start their economies and suggested that the European Central Bank should lower interest rates because of falling inflation.