Petroleum contains many hydrocarbons, with chains of different lengths. Octane (C8H18) is one. Refineries separate various hydrocarbons. In principle a refinery can separate pure octane. If sold at the pump, that would be by definition gasoline with 100 octane rating. The majority of the hydrocarbons are worse than octane, but some are slightly better. So you could have gasoline without any additives that has an octane rating slightly higher than 100. The problem is that most chains have octane rating significantly lower than 100. What do you do with them? You throw them? Of course not. People create different blends, and add some additives so they can sell as much of the original petroleum as gasoline with a decent octane rating.
Yes, there are some other octane boosters. The main ones today are 3: ethanol, MTBE and ETBE. MTBE and ETBE are derived from methanol and ethanol respectively [1]. I don't know if there is anything wrong with MTBE or ETBE, but the ethanol lobby managed to push the idea that ethanol is good, so it is widely mixed in gasoline in the US.
According to the DOE [2]:
Lower-octane gasoline is blended with 10% ethanol to attain the standard 87 octane.
Yes, there are some other octane boosters. The main ones today are 3: ethanol, MTBE and ETBE. MTBE and ETBE are derived from methanol and ethanol respectively [1]. I don't know if there is anything wrong with MTBE or ETBE, but the ethanol lobby managed to push the idea that ethanol is good, so it is widely mixed in gasoline in the US.
According to the DOE [2]:
[1] https://en.wikipedia.org/wiki/Methyl_tert-butyl_ether#Altern...[2] https://afdc.energy.gov/fuels/ethanol_fuel_basics.html