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I think Mikey_s is our man here, because I haven't the slightest idea if this figure is for oxygenates present in gasoline.
IF they are, this oxygen is present in "pre-used" fuel molecules, that is, fuel that is already bonded with an oxygen atom, like ethanol.
Oxygen in fuel cannot provide energy, so these fuels produce less energy output per unit of mass or volume.
I think they are used because they provide a reasonable anti-knock value and they replace the high octane aromatics you use in some fuels for the same purpose.
On old engines, without stochiometry management, oxygenates reduce the HC and CO emissions, because the engine will move to the "lean side". Just a bit of oxygen in the fuel (2%) can reduce smog and contamination by significative amounts (16% reduction in CO and 10% reduction in HC). That's the reason why we use them in my country.
On newer engines, the computer will increase the amount of fuel used to achieve the preferred stochiometric value of the fuel mix, so you use more fuel. On the positive side, some modern engines are more efficient with this kind of mixtures, but not efficient enough to compensate for the extra fuel that the computer throws into the cylinders.
These compounds are also preferred to the old tetra ethyl lead for anti-knock, because lead makes you dumb and sick (that's the reason why oldies here have so few neurons working at full capacity: too much lead during our infancy and youth).
There are other compounds for anti-knock, but they are banned (because they're worse or similar to lead compounds) or wear the engine more than the ones currently in use.
Now, I could be completely wrong. Let's wait for Mikey or some other expert to be sure.
