World oil markets are likely to remain under pressure for some time before high prices have a corrective impact on both supply and demand, says Simon Johnson, the chief economist of the International Monetary Fund.

"Over the past six months, as the global economy has slowed, the prices of most kinds of commodities have moved up rather than down-that is, doing the opposite of what we would ordinarily expect," Johnson points out.

He adds that, "although the more recent increase in energy and food