Henry's Law: $C^* = p_{O_2} / H$ (or equivalently $p = H \cdot C$), where $H$ is Henry's constant (atm·L/mol). As $p_{O_2}$ increases (e.g. by pressurising the reactor or using oxygen-enriched air), $C^*$ increases proportionally. At 37°C, $C^*$ in water at air saturation ≈ 0.2 mmol/L. This low solubility makes oxygen supply the most common limiting factor in aerobic fermentations.