The amount of ${\text{O}}_2$ normally carried by $100\text{ml}$ of pure oxygenated human blood is:

Under normal physiological conditions, each gram of hemoglobin ($\text{Hb}$) can bind to approximately $1.34\text{ml}$ of oxygen (${\text{O}}_2$). Since normal healthy human blood contains roughly $15\text{g}$ of hemoglobin per $100\text{ml}$, the total oxygen-carrying capacity can be calculated as follows:
$$\text{Oxygen carried}=15\times 1.34\text{ml}\approx 20.1\text{ml}$$

Therefore, $100\text{ml}$ of pure oxygenated blood carries about $20\text{ml}$ of oxygen.