FOR the first time since 2009, the economies of major developed countries are shrinking.

The Organization for Economic Cooperation and Development, a group of 34 countries, said this week that the combined gross domestic product of its members declined at an annual rate of 0.6 percent in the final three months of 2012. It was a sign of just how far the global economy has weakened since 2010, when it appeared that the recovery was gathering strength.

The estimate was preliminary, since not all countries have released figures for the quarter and those that have will be revising them. The United States, which reported a small decline of 0.1 percent in the quarter, is expected to revise that to show a small gain when it reports new figures next Thursday.

It is unusual for downturns to be so widespread that they produce declines in the combined economies of the O.E.C.D. countries, which include all the major developed nations. Since 1962, when the O.E.C.D. statistics were first released, there have been only 13 quarters when that happened. The first three were in 1974 and 1975, during the worldwide recession brought on by the shock of soaring oil prices. There were four more in the early 1980s, during the double-dip American recession, one in 2001 and four in 2008 and 2009, during the credit crisis.

On Friday, the European Commission issued a glum forecast, saying the 27 countries in the European Union would see economic growth this year of just 0.1 percent, while the euro zone economies would shrink by 0.3 percent. If the O.E.C.D. estimates are correct, each of those forecasts would represent an improvement from 2012. During the four quarters of 2012, the O.E.C.D. estimated, the economies of the entire European Union declined by 0.6 percent, while the euro zone economies were down 0.9 percent.