I can get 22-23 mpg city if I work at it. By that I mean VERY gradual acceleration, and putting it in neutral to coast up to red lights. If I drive like the average driver, it drops to 20 pretty quickly, or even lower. A lot also depends on the route I take and how lucky I am hitting the lights. Highway, about 35 mpg, give or take. I made it to San Diego and back (about 950 miles) on a tank and a half.

My best average so far, for a day of around-town driving, has been 23.4.

I use Bell Mix-I Go and have for several years.

I don't necessarily follow "there menu" but I do put a double dose in a fresh full tank of fuel twice a year or approx. every 10,000 miles.

It is a great quality product.

Silverfox

Our 07 2.2 avgs 28 mpg mostly city with a little expressway , can get low 30's on long expressway trips.
The 08 SS avgs 25 mixed and gets 28 on long expressway trips.

My Info Center almost always reads right at 20 to 22 mpg.
the most gas i get at bout 150 miles is 7 to 8 gallons.
Not bad for driving streets with some steep arse hills
while throwing news papers.

Just drove 3,400 miles in ten days hills , highway, A/C on traffic jams and 85 MPH runs for a short but. From Buffalo NY to Mediera Beach FL. Three adults and luggage! Avg MPG 30.4!
Same drive last year with a blown out flex joint 25.7 mpg

My 09 SS with a custom tune gets 31 on highway trips. In town for work i get 26-28.

Hot Rod Power Tour this summer for me was 1374.5 miles that included a day at the drag strip making several passes, several instances of showing off and being stupid, and lots of sitting in line with the a/c blowing. 29.476mpg average. Not bad for a car making 400+hp

Getting 27 in town and 33 highway.
2008. 2.2 auto, and it's supercharged.

I wonder why my intown mileage is so low(20-21mpg) compared to what people on this site claim. On the highway I do alright(29-33, usually around 31) on 70mph roads and 35+ on 55mph roads. And it is better to use the gas peddle instead of cruise control unless the road is fairly level. I have a 2.2L with 51k miles. The airfilter is a K&N with the K&N airbox and is oil correctly. There is no blockage in the wooly worm. I figure my mileage with a pencil not what the DIC says an that is too easy to manipulate. By manipulate I mean for example: I leave home and reset the mileage average and go a few miles and return home babying the gas pedal all the way, and wah-la I get 25-29 mpg in town. That's not right, I'm not fooling anyone but myself unless I just want to take a picture of the DIC and claim that's my intown mileage. It's not...by later today it will be down to 20-21 if I drive a few more miles. I mean 20-21 mph is not terrible but it certainly is not what others are getting.
IS THERE ANYTHING I CAN CHECK TO FIND WHY I CAN'T SEEM TO GET THESE GOOD MILEAGES EVERYONE ELSE SEEMS TO BE GETTING ON THEIR HHR?

Time for old school investigation, pull the plugs , what colour are they, do the gaps all look the same?
What brand are they, AC Delco 41-103 seem to the favorite of any 2.2 Ecotec I've worked on in the last 12 years
Then let's go from there, I know you know but I have to put this out there,
Do Not attempt to gap your Iridium spark plugs!!!!! They will break very easily!!!!!
Look but don't touch!!!
There now I feel better!