What sort of unleaded Gas do you use?

87 at Citgo mostly. The stuff at Wal-Mart has been OK when price mattered more...

 

87 Only (Or 85 in the Mountains if that's all there is)

Anything else can lead to check engine lights and other undesirable things.

 

Liquid unleaded gasoline works best.

 

Owner's manual. 87 unleaded.

Octane is not a measure of how much power the gasoline has, but how resistant it is to combustion.

Higher resistance (octane) is needed in higher-compression (higher HP) engines to prevent knocking which the Prius engine isn't.

Of course the Prius engine can probably adjust to higher-octane gas, but wouldn't get more mileage/power so you would be just wasting money, and possibly building up deposits in the engine/exhaust.

 

My Prius currently has a tank of 87 Octane Costco gas in it. Car seems happy enough, so I won't argue with it.

 

Yep, 87 is just fine and dandy for this wonderful car. There have been a few documented cases on here where drivers have tried higher octane fuels for a few tanks to show there was no increase in MPG.

-m.

 

Not combustion but detonation or preignition. Big difference! Detonation is uncontrolled combustion which is very harmful to the engine in that the fuel mixture ignites prematurely and in an uncontrolled fashion. This can wreak havoc on the pistons. The audible result of detonation is what used to be called "ping." I believe today's engines have sensors that detect detonation and retard the timing, as required, to protect the engine.