What octane is
Resistance to knock (premature combustion under compression). Higher octane burns later. Useful for high-compression engines like turbo or performance. Pointless in low-compression engines.
The myth
Premium ‘cleans’ the engine. All gasoline meets the same baseline detergent standard since the EPA mandate in 1995. The ‘cleaning’ claim is marketing copy from the 80s.
When to use it
If your manual says ‘premium required.’ ‘Premium recommended’ usually means you can run regular with a tiny power loss; do the math on the per-tank cost vs. the loss.