Hmmmm.... Ok, I think there are several things that affect this:
1) altitude
2) temperature
3) local topography
4) local wind patterns
5) passenger, weekender or camper van
6) state of tune (ha ha)
7) driving style

Now I bring this up because obivously everyone lives in a different
environment, so it's all kind of moot anyways.  I live at moderately
high altitude (3500 ft), low humidity usually, cold (hey, it is Canada),
very hilly (Foothills of the Rockies), lots and lots of wind (spend a
lot of time hammering into 40 to 55 mph headwinds), drive a 1986
Westfalia, engine not quite running 100% but runs well, and I am too
used to driving my 98 Golf, so I never drive my van in a relaxed and
patient manner, and most of the driving is mixed city/highway.

I've had my van for about 9 months now.  Worst tank of gas 12.8 mpg
(US).  Best tank 18.1 mpg (US).  Average 15.9 mpg.  Total mileage 4524
miles since we got it.  Total miles on van are 165K miles.  Never had it
on an extended, all highway road trip to see how the mileage fares.
Driving to Yellowknife, NWT in July, so that oughta do ;-)

Honestly, I find my mileage is more influenced by whether or not I'm
pushing a wind.  Tailwind = good mileage.  Headwind = total crap
mileage.

YMWUV (Your Mileage Will Undoutably Vary)
Keith Adams
Calgary, Alberta, Canada
1986 Vanagon GL Westfalia "Roxy"

Mick Kalber wrote:
>
> I've had three vanagons... an 86 gl, an 88 wolfie gl, and now an 89 syncro
> westy.  Every one has gotten between 17 and 18 MPG no matter where or how I
> drive.  I'm sure there has been some variation between city and highway, but
> not much in the overall.  Always thought the consistency was interesting.
> Your mileage may, and apparently does, vary.
>
> Mick Kalber
> 89 Syncro Westy "Daddeo"