(FORTUNE Magazine) – TWO WAYS TO MEASURE To compare incomes among countries realistically, you have to adjust for what a given sum of money can buy in each. That's what University of Pennsylvania economists Robert Summers and Alan Heston do with their purchasing-power calculations. But the unadjusted numbers in column two give a better picture of each country's buying power in the world marketplace. Rankings can change abruptly: Rising oil production has pushed the United Arab Emirates to the top of the list.

CHART: NOT AVAILABLE CREDIT: SOURCES: PENN WORLD TABLE, WORLD BANK, WEFA CAPTION: NO CAPTION