One dude used to post in here some fantastic figures for highway mpg for
a mid 90's Buick Park Avenue. He claimed he kept in at around 55 -60 mph
on the highway did, some coasting on down grades and got 34 to 36 mpg. I
think he lived out west somewhere.

Seems like it be suicide driving 55 - 60 mph on the Chicago
expressways...lol. I bet he got some mean looks and horns blown at him.

I get 27 - 29 mpg on the highway doing 72 mph in my 05 Buick 3800.

Bonneville highway mpg is 26 - but its not used much on the highway
anymore.

Good Luck

Harryface

05 Park Avenue 37,229
91 Bonneville 306, 311

I have a '98 GP with the 3800 engine that's been maintained beautifully,
and if it gets 34 mpg hwy, it'd have to be rolling down a steep grade
with a good tail wind. 25-27 mpg hwy is more like it.

We've had it since 2000 - no problem with the gaskets (knock wood).
Drove an '06 when we were out of town a few months ago - it's pretty
sweet, but I surprised how much smaller the backseat is between the new
ones and my last century model!

On long trips I get around 29 mpg at 75 mph or so. That's with a fair amount
of luggage and such.

I only get 20-21 in my normal suburban driving though, and I'm not usually a
lead foot. Hell, at $3.19 for premium, who is a lead foot?

Lee
'00 SSEi

I have an '06 GP N/A, same color scheme.  I just got back from a
400-mile round-trip drive, got 26.6 using pen-and-paper.  I only 7,000
miles on the odometer and am using Mobil 1.  I love being able to go
to my brother's and back on one tank of gas.  The trip home was windy,
if it wasn't so bad I might have gotten better MPG, the trip computer
read 28.5 when I left my brother's house.  I drove the whole way home
non-stop, just over 3 hours, no comfort issues here.  I have pics of
some subtle appearance mods that make the car SWEET looking and make
it stand out.  Total cost was under $400 for what I've done.  I'll
post a link if you want.

I have a 2001 Pontiac Grand Prix with a 3.8L V6 without the
supercharger.  I make two 2-hour trips per week, so I get a lot of
highway miles.  The lower MPG values were weeks I did not make either
of my 2-hour trips or just one of them.  The highest MPGs were when I
did about 78 MPH during my trip.  I noticed a .3 to .5 decrease in MPG
when driving 83 MPH versus 78 MPH on my trips.  Here is some of my data
for gas mileage:

Avg. Gas Mileage:  23.90

Miles    Gallons    Gas Mileage
341    13.947       24.45
348    14.244       24.43
368    15.936       23.09
402    16.275       24.70
284    11.619       24.44
337    14.074       23.94
397    16.435       24.16
373    15.767       23.66
364    15.222       23.91
370    16.28       22.73
391.5    15.962      24.53
326    15.131      21.55
367.1    15.482     23.71
328    14.151      23.18
93.2    3.603       25.87
367.5    15.808     23.25
375.5    15.872     23.66
332.2    13.546     24.52
352.5    14.25      24.74
261.5    11.035     23.70
386.5    16.385     23.59

Glad to see you're happy with your GP.  I wish I could say the same about my
'04 GT1.  So far it's been nothing but trouble.  The steering wheel had to
be replaced after repeated attempts to get the horn of all things to work
properly and even the NEW replacement steering wheel had to be tweaked to
get the horn to work like it should.  The A/C air recirculator failed and
had to be replaced.  The service crew at my dealer screwed up the fix for
the A/C by forgetting to replace the shroud that keeps rain from getting in
the cabin.  It rained after the work was done and flooded the car.  I didn't
know about it until days later when I got around to driving the car.  There
was about 5 gallons of water on the passenger side.  The dealer felt so bad
he replaced the carpet padding for free.
The steering shaft had to be replaced due to some clunky noises.  7000 miles
later the noises came back and this time it was out of warranty by only 3 or
4 thousand miles.
But by far my biggest pet peeve as far as the '04 model year is concerned is
that I get horrible sun glare reflecting in my eyes from the bottom of the
instrument cluster's Plexiglas shield.  It happens when the sun is directly
overhead during the midday hours.  I can't find a seating position where I
can avoid it.

The GP has only 39,000 miles on it and it's been more trouble than the old
'96 Escort LX I had with 150,000 miles.

GM

I've got a 95 generation 3 3800 that gets about 25mpg on average.  It's
in a Olds 88 Royale.  I don't do a lot of expressway driving, but even
when I do it stays in that ballpark.