The World Gold Council’s third-quarter demand report on Thursday showed central bank buying reached nearly 150 tonnes, far above most analysts’ estimates, but the buyers were not named. According to an analysis by Reuters of IMF data, previous buying patterns and delays in data reporting, the most obvious candidates are China and India.      Judging from the trend over the last two years, the purchasers are almost certainly nations with large external surpluses and big foreign exchange reserves, the bulk of which are in the emerging world, with nations in Asia or Latin American being the most likely. According to Reuters calculations based on data from the International Monetary Fund, central banks have bought a net 208.9 tonnes of gold so far in 2011. The IMF data has identified buyers for a net 20.0 tonnes in the third quarter, creating a mysterious discrepancy of nearly 130 tonnes. The WGC, an industry group, said it could not reveal the names of the buyers for reasons of confidentiality, which only added to the intrigue.   So far this year, the biggest buyers of gold have been Mexico, Russia, Thailand and South Korea. Other smaller, but nonetheless noticeable, buyers by virtue of their habitual absence from the market, include Colombia and Bolivia. The list of the countries with the largest foreign exchange reserves is easy enough to come by. China, Japan, Russia, Saudi Arabia, Taiwan, India and South Korea are among the biggest. Filtering through the reams of data the International Monetary Fund releases every month, however, is more complex and becomes a process of elimination, as many nations do not report changes to their gold reserves to the IMF on a regular basis. This year’s three top buyers all report on a monthly basis and include any changes. So who has the firepower to buy that much gold and who doesn’t report every month to the IMF? The sudoku that are the IMF’s international finance statistics shows that in Asia, among the most likely candidates is China, which has the largest currency reserves, at $3.2 trillion, and reports its bullion figures with a two-month delay. The snag here is China does not necessarily include the changes to its reserves when they happen. China said in April 2009 its gold holdings had risen to 1,054.4 tonnes from 600.3 through purchases that took place between 2003 and 2009.