Because of differences in living standards, and therefore in capacity to pay, some countries will be expected to shoulder larger shares of the total costs of providing global public goods, which may reduce their incentive to cooperate in providing them. Hence, with respect to establishing multilateral agreements, the pattern of burden sharing will be as important as the extent of the benefits to be conferred by the public goods. I am grateful to my staff at the Development Policy and Analysis Division for their research and work going into those studies. They are not responsible for any remaining errors and the views expressed in this paper do not necessarily coincide with theirs neither with those of the United Nations. The trends are starkly unambiguous when China is not included (Bourguignon and Morrison, 2002, Milanovic, 2005 and World Bank, 2006). The number of megacities increased from 10 in 1992 to 21 in 2010.