Businesses in the U.S. expanded in December at the fastest pace in two decades, adding to evidence the world's largest economy is accelerating heading into 2011.

The Institute for Supply Management-Chicago Inc. said today its business barometer rose to 68.6 this month, exceeding the most optimistic forecast of economists surveyed by Bloomberg News and the highest level since July 1988. Figures greater than 50 signal expansion.

Gains in business investment on new equipment and growing exports to emerging economies will keep factories churning out goods in the coming year, contributing to the recovery. Reports showing consumer spending is also picking up mean retailers will need to restock shelves, giving manufacturing a further lift.