| Member country | Area of the country within MRB (km2) | As % total area of the basin (%) | As % total area of the country (%) |
| China | 165,000 | 21 | 2 |
| Myanmar | 24,000 | 3 | 4 |
| Laos | 202,000 | 25 | 85 |
| Thailand | 184,000 | 23 | 36 |
| Cambodia | 155,000 | 20 | 86 |
| Vietnam | 65,000 | 8 | 20 |
| MRB | 795,000 | 100 |
|