As gas prices rise, your car's engine efficiency is an important consideration. You might consider paying the premium for high octane gas to keep your engine running better longer, but does a high octane gas necessarily translate into a more efficient engine?
The short answer is probably not. The recommended octane for most cars is "regular" octane gas: 87 to 88 octane. Check your car's owner's manual to see the exact recommendation.
Octane ratings measure a gasoline's compression ability. Normally, the fuel-air mixture in the engine is compressed and then ignited by the spark plugs. But if that mixture is compressed too much, it will ignite spontaneously, which results in engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in an engine cylinder.
The higher the octane, the more the gas can be compressed without spontaneous ignition. The more it's compressed, the more power it will produce. However, simply adding high octane gas to your engine will not cause it to compress that fuel-air mixture any more than it does with regular gasoline, so you get no benefit for the extra money you spend.
When might you want to consider the high octane gas? Some high-performance, high-horsepower sports cars and luxury cars require a mid- or high-grade gasoline; check your owner's manual to make sure. You might also consider switching to a higher octane if you experience consistent engine knock with the recommended octane level.