In a prior post I discussed making the switch from Chevron 93 supreme to Shell V-Power. Gas mileage appears to be identical using either brand. I am averaging ~22 mpg for city driving, with most trips being 5 miles or less. This does not seem to be too good when one considers the 30 mpg rating for city driving that Honda lists on the window sticker. Of course I only have about 650 miles on the car, so maybe my mpg will improve over time. Shell V-Power continues to impress me. I can notice a difference when using V-Power even if the mpg is the same as Chevron. My car is quicker to accelerate and seems to maintain speed with less effort. These opinions are subjective of course. I am about 5 miles away from the Shell Deer Park refining complex where they make some of their gasoline, so perhaps that has something to do with it.

 

22mpg seems low but your car is new. wait a while and it should go up.

im hitting 8k miles and finally seeing 30 mpg. i was seeing 25-27 before

 

You would very likely get better mileage with lower octane as the motor was designed for.

 

Here are a few things you should consider:

1) 30mpg is an inflated number, it's difficult to get 30 mpg all city. The new fuel economy tables, at fueleconomy.gov, list the base Civic's mpg as 25 city, to take into account faster acceleration, air conditioning, etc. For example, my Accord only gets 20 mpg city. The old EPA was 23, the new EPA number is 20.

2) The Civic was meant to operate on 87 octane gas. The only difference between 87 and 9x are any detergents the stations put in and the fact that it is harder to detonate. By having a fuel that is more difficult to detonate in your engine, it won't run optimally, costing you more fuel. The detergents are really similar so you'd be better off just buying the 87 and putting in a detergent additive if you feel so inclined.

 

The compression ratio of the 07' LX is 10.5:1, which seems to indicate that a higher octane fuel may provide a small increase in performance. The owner's manual states that 87 octane, or higher, gasoline should be used. There is no mention of higher octane gasoline resulting in a decrease in mpg. I like to use 93 octane due to the frequent short trips that I make. The extra detergent additive in 93 octane gasoline provides me with peace of mind. It only costs me about $2 per tank to use 93 octane and I only fill up my car about every three weeks. I know that my car will operate perfectly fine on 87 octane gas though.

 

I run 87 on my 07 LX and I get 27mpg all the time with about 50/50 city/highway. Just under 5k miles on the car and nearing the 1st oil change. You should give 87 a try and see if it differs any.