The retail sellers think they won't even have enough to fill all customer orders placed months ago, reports the Seattle Post-Intelligencer.
Some conspiracy enthusiasts think Microsoft is holding back on shipments to create an artificial appearance of extraordinary demand, the report said.
Xbox executive Peter Moore denies such theories and says it is due to the unprecedented scope of the launch.
The console, designed to challenge Sony's dominant PlayStation franchise, is being launched in North America, Europe and Japan in rapid succession, over a span of three weeks.
Worldwide, Microsoft expects to sell 3 million Xbox 360 units in the first 90 days of issue.