CO₂ is carried in three main ways:

1. Dissolved in plasma:  about 7% of CO₂ dissolves directly in blood.
2. As carbaminohaemoglobin: about 20–25% binds with haemoglobin.
3. As bicarbonate ions (HCO₃⁻): about 70% is transported this way, formed when CO₂ reacts with water in RBCs.

This bicarbonate transport is the most important.