Please state your engine size and year of the car.
Mine seems to produce more power with 89 octane. Didn't seem to enjoy 87 and 91 as much.
I know there was another post on this sometime back, but most of us now have some miles under our belts with our new bu's and have gone pass the break in periods.

3.6L , 2008 2Lt

2008 LTZ, 3.6L, 6 Spd

Manual calls for Regular (87 Octane) and that's what she gets. Whenever possible I use a Top Tier Gasoline (http://www.toptiergas.com/) to help keep things clean, if not, then she gets a shot of Chevron Techron.

I have the 3.6 as well. I thought the manual said 89 octane but 87 "could" be used. I need to re-check.

3.6L V6 - 89 octane with 93 used every once in a while.

I'm glad someone asked as it forced me to go back and look at the manual. For the 2009 3.6l, it says 87 is OK but for towing or best performance, use middle grade 89 octane. That means the ECM has timing tables with sufficient range to take advantage of a little more octane. That would tend to validate the original posters comment that 89 worked best for them.

For the 2.4l, it just says 87 or higher.

we use 89 octane in our malibu. If get the best performance and fuel milage.

Mine came with an owner's manual. It says 87 octane, 89 for optimum performance.

I put 87 in there but once I get home from my deployment I will start putting 89 octane in her... I gotta see how much better performance and fuel mileage I get.

I will have to try and see what I get. The 4 cyl. may not get much help from it (89).

3.6L 2009 LT2, gets 89 octane

I had no idea 89 is recommended...Never occurred to even check the manual on that, so i've been using 87.

http://www.straightdope.com/columns/read/2565/whats-the-difference-between-premium-and-regular-gas
http://en.wikipedia.org/wiki/Octane_rating

http://www.straightdope.com/columns/read/2565/whats-the-difference-between-premium-and-regular-gas
http://en.wikipedia.org/wiki/Octane_rating

Good reading for a little background info.

I use 87 in my LS. Try to stick with Top Tier brands, and I usually run a dose of Techron cleaner every 10K or so. No mileage/power differences on 89 or 91.

I too did not realize there was a recommended grade and have use only 87 so far. I put in 89 yesterday and doubt I'll notice a difference (got about 370 miles on the last tank) but will try it out to see what happens, and will post any definite findings.

Good reading for a little background info.

I use 87 in my LS. Try to stick with Top Tier brands, and I usually run a dose of Techron cleaner every 10K or so. No mileage/power differences on 89 or 91.

Anything above 89 octane would be a waste for sure. I will try 89 myself but it will take a couple of tank fulls to make any comparisons.. I always use Chevron and I did get better mileage with Chevron than with generic gas on my previous car at the same grade.

89 octane for me.

I've been using 89 and it does perform better when I used 87 the first couple of weeks had the car.