Smu,

From http://www.cia.gov/cia/publications/factbook/index.html

The US's GDP in 2000 was $10 trillion.
The gross world product in 2000 was $43.6 trillion.
It's not quite 1/4.

"The US economy continued its remarkable sustained prosperity, growing at 5% in 2000, although growth slowed in fourth quarter 2000; the US accounted for 23% of GWP. The EU economies grew at 3.3% and produced 20% of GWP. China, the second largest economy in the world, continued its strong growth and accounted for 10% of GWP. Japan grew at only 1.3% in 2000; its share in GWP is 7%"