2 Answers

This following is a list of the ten longest rivers in the world, according to the Times Atlas of the World.
1. Nile River - Africa - 4,160 miles - 6,695 km
2. Amazon River - South America - 4,049 miles - 6,516 km
3. Yangtze River - Asia - 3,964 miles - 6,380 km
4. Mississippi-Missouri River System* - North America - 3,709 miles - 5,969 km
5. Ob-Irtysh Rivers - Asia - 3,459 miles - 5,568 km
6. Yenisey-Angara-Selenga Rivers - Asia - 3,448 miles - 5550 km
7. Huang He (Yellow River) - Asia - 3,395 miles - 5,464 km
8. Congo River - Africa - 2,900 miles - 4,667 km
9. Rio de la Plata-Parana - South America - 2,796 miles - 4,500 km
10. Mekong River - Asia - 2,749 miles - 4,425 km

* The Missouri River is, hydrologically, the upstream continuation of the Mississippi River as the Missouri River carries more water than the Mississippi River at the confluence of the two rivers.

http://geography.about.com/od/lists/a/longestrivers.htm

Nile   6650 kilometers
Amazon  6400
Yangtze  6300