Lengths for major rivers are approximate — a river's "true" length depends on which headwater stream you count as the source, so different atlases disagree by a few hundred kilometers. The Nile vs. Amazon question for #1 is the classic example: some measurements would flip the order. This is the traditional ranking.
- Nile — Africa — ~6,650 km (4,132 mi)
- Amazon — South America — ~6,400 km (3,977 mi)
- Yangtze — China — ~6,300 km (3,917 mi)
- Mississippi–Missouri — USA — ~6,275 km (3,902 mi)
- Yenisei–Angara–Selenge — Russia / Mongolia — ~5,539 km (3,442 mi)
- Yellow River (Huang He) — China — ~5,464 km (3,395 mi)
- Ob–Irtysh — Russia / Kazakhstan / China — ~5,410 km (3,362 mi)
- Río de la Plata–Paraná — South America — ~4,880 km (3,032 mi)
- Congo — Africa — ~4,700 km (2,922 mi)
- Amur–Argun — Russia / China / Mongolia — ~4,444 km (2,763 mi)
Even though the Amazon is usually ranked #2 for length, it wins the more lopsided record by far: it carries more water than the next seven-largest rivers on Earth combined.