An expert committee of architects has been studying New York's new World Trade Center tower and Chicago's Willis Tower.
Backers of both buildings claim theirs is the tallest.
The Height Committee of the Council on Tall Buildings and Urban Habitat is expected to announce its decision this morning in Chicago.
The committee is recognized as having the final say on building heights around the world.
It's been weighing whether a design change means the needle atop 1 World Trade Center is part of the actual building or merely the equivalent of a broadcast antenna.