Under ideal conditions a common internal combustion engine burns the fuel/air mixture in the cylinder in an orderly and controlled fashion, as part of a “four-stroke cycle”.

Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. It causes excessive heat, pressure, and stress on the piston, cylinder head, valves, spark plugs, and gaskets, leading to cracks, holes, or melting and severe engine failure eventually.

One way of addressing knock is using high-octane fuels, as octane is the key parameter indicating the fuel performance in an gine. The octane number, also called RON, measures how good a petrol is at resisting premature ignition in the engine. Increasing RON while reducing CO₂ footprint of the final petrol product is possible thanks to ethers: in higher octane petrols (e.g. 98 RON) the GHG reductions for oxygenated fuels with ethers range from 7–10 percent.

In all of these scenarios, the ETBE blends provide the larger CO₂ reduction, owing to the higher amount of reformate replaced.