I get 15 mpg in the city, too. Short drives, mostly surface streets. Makes no difference how I drive, although higher tire pressures seem to help.

 

With reference to driving at high altitudes, less dense air means the car will put MORE fuel into the fuel/air mixture to keep the engine running. Trust me....I'm a pilot

 

Well, I believe the computer tries to maintain a constant air/fuel ratio (when I say "air" I mean oxygen) for optimal combustion. Too much fuel is called a "rich" mixture and does bad things to your engine. At higher altitude, there is less oxygen for a given volume of air, thus the computer meters less fuel per volume, thus higher MPG. The downside is you make less power. Not only is this a theory, it's born out by real-world experience. If I take my car down to sea level, say San Diego, I make much more power but get much worse fuel mileage. I've lived in Colorado for over 20 years and have driven the same cars here at altitude as well as at sea level, and this is what happens. Trust ME...I am a pilot, too!

 

I typically average around 25 mpg with my commute being a 20 mile, point the car down the road at 60 mph. I have seen a high of 34 mpg (two tanks of fuel and using the odometer) on a long interstate trip keeping between 65 and 70 mph. That said, as soon as you include any local driving the average goes to heck. The car is heavy and takes a lot to get it moving yet it will roll forever once up to speed (I have a manual).

 

I drive in hawaii as well. my 2006 550i gives me only 12.1mpg
New tires, all services up to date and city driving with a lots of traffic.
Did you code your car?

 

What do you mean code my car?

Yeah, Hawaii traffic man....horrible!

 

Are you fueling 91 or higher cause that makes a difference, If you do then try with a max flow air filter but make sure you buy it from the actual dealer and not some shop, sometimes the air flow would be too high and will set of a lean code. And also at the dealer they have this liquid that you add to the fuel tank, It should help a little, if not then you need a tune up. Hope this helps

 

I've seen my fuel economy drop below 20mpg when stuck in very heavy NYC/DC/Phila city traffic. Since I rarely deal with more than 10-20 miles of that at any time the gas mileage experience w/my '07 530xi [60k+ miles]isn't a direct comparison for you. That said, I've never recorded trip mileage as low as some noted in this post - NOT EVEN in my '01 740Sport! I must be a ultra-conservative driver

 

Thank god im not the only one! I was doing 13~ around town and thought there was something wrong with my car. I went from wonderful gas mileage in my E39 528 and 530 i to terrible in my 550i. Of course i can blow the doors off of both of them by 10 fold.

 

Coding your car in order to activate more features. like all windows up with key fob, angel lights on with key etc.

Honolulu's traffic sucks! moreover, I live in waikiki.