OPEC is getting increasingly worried about global oil demand this year, potentially setting the stage for another round of production cuts next month.

In its latest monthly oil-market report, the oil cartel took a machete to its demand forecasts for 2009, just as the rich-country energy adviser IEA did this week. OPEC cut its global oil-demand forecast by 530,000 barrels a day compared with its outlook just one month ago.

They...