Final answer:
One technique used to increase the octane rating of gasoline is the use of octane enhancers or antiknock agents, such as tetraethyllead, MTBE, and ethanol.
Step-by-step explanation:
One technique that has been used to increase the octane rating of gasoline is the use of octane enhancers or antiknock agents. These additives are designed to reduce or eliminate knocking and pinging in a combustion engine, which can result from premature combustion of the fuel. One widely used octane enhancer was tetraethyllead, but it has been phased out due to its toxic nature. Other enhancers such as methyl t-butyl ether (MTBE) and ethanol have been developed as alternatives.