As an experiment, I used 92 octane premium gas in my last fill-up. Interestingly, my MPG jumped from about 49 (after 2 fill-ups at 87 octane) to 58.7 octane this time (after the 92 octane fill-up). Similar driving patterns and routes.<br><br>If this continues to hold true, the higher cost of 92 octane gas would more than pay for itself (but not by much) in better mileage.<br><br>GCKorn

&lt;&lt;&lt;&lt;&lt;&lt;&lt;Wow, that's a big difference! Do you really mean you went from 49 to 58.7, or was there a typo?&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;<br><br>I really mean it. I keep scrupulous track of gasoline usage on an Excel spread sheet. If you forward me an email address, I'll post it to you.<br><br>Actually, the prior two fill-up ratings were 48.0 (which included a highway trip, so it doesn't count) and 47.4 (which was the same as this most recent 58.7 fill-up.<br><br>Now, I'm sure part of the difference is attributable to driving variations (fewer red lights, less traffic). But part may well be due to the octane. I'll try it for another few tanks and see what develops.<br><br>GCKorn

John,<br><br>1. First, I absolutely LOVE your Prius site and pics. Keep 'em coming!<br><br>2. Second, the jump I experienced from 48 and 47.4 (two fill-ups after 87 octane) to 58.7 (this fill-up, after 92 octane) can't all be octane related, as I said in my prior post. The whether also cooled down a bit, so I used the vents less. As electricity usage is a drag, this probably also factors in. That said, I clearly "sensed" from my constant MPG video-gaming that the car was running more efficiently, at at a higher MPG rate, what with the 92 octane in the gas tank. <br><br>3. I'd sure like to know if I'm dreaming this or if octane really can help with mileage.<br><br>GCKorn

I took a moment to go to an oil company web site and get a little info for you on octane. I have no intrest in Chevron, feel free to check other oil company sites for additional info.<br><br><a href=http://www.chevron.com/prodserv/frame.html target=new>http://www.chevron.com/prodserv/frame.html</a><br><br>This site does a good job of explaining octane.<br><br>To answer your question of increased milage, it is possible. The specific gravity of the fuels could be different, giving you more energy in each gallon. And/or the sophisticated electronics in the hybrid system may be able to take advantage of the timing advance allowed by higher octane ratings, giving better efficiency.<br><br>The different grades of gasoline are manufactured to government specs and should be very similar from grade to grade and manufacturer to manufacturer. <br><br>This is also the time of year when the oil companies switch from summer formulations to winter. The specific gravity does change in this summer/winter switch.

Does anyone know if the higher octanes burn any cleaner? I would be willing to pay even a little more for the higher octane if it makes a difference for emissions.<br><br>Martin

If you are getting better mileage, then I would assume you are emitting less from the tailpipe. However I wonder about the production process for making high octane gas. Does it produce more waste at the refinery?<br><br>Bob F

Regarding Octane Improvements:<br><br>According to the Prius New Car Features manual, the resin tank shrinks 5 liters in volume when the temperature drops to 14F (10C). This is a considerable difference in volume. (I notice that they don't give the temperature they are comparing to though...not good science.)<br><br><br>As Fall rolls around, perhaps the increase in mileage may be more attributed to this shrink (due to lower Fall temps) than octane. Obviously keeping records over several tank fillups will perhaps minimize some of this temperature effect. Mileage calculated from only one fillup though needs to be put in perspective.<br><br>Next Spring may cause all the mileage figures to change again (decrease) as the temperature warms up.<br><br>Pete