I like having fun with my Altima. So on a Road Trip to Utah in December of 2007, and in no hurry whatsoever to get there, I decided to see what the 2007 2.5 liter 4 cylinder Nissan Altima fuel mileage potential is.
Here are my results:
Click on any image to see a larger, more detailed picture.

I started out near Victorville CA instead of my home town in Los Angeles because I didn't want to mess up the mileage by going over the mountains right off the bat.
So I filled up at a gas station in the high desert and immediately got on the freeway driving pretty much as slow as safely possible.
I slowly accelerated to 55 MPH and set the cruise control.

I decided to document everything and started taking pictures at about 63 miles into the trip.
I drive at 55 for what seems like forever watching all the big semi trucks pass me and only accelerating hard a couple times to avoid causing anyone to nearly hit my rear-end.

Somewhere in here I got pulled over for having my front windows tinted at 5% (limo tint) JUST 2 DAYS AFTER GETTING A TICKET IN HOLLYWOOD FOR THE SAME THING! But of course I didn't have the Hollywood ticket in my car to show the officer so he wrote me up another one.
I wonder what the officer was thinking when he saw me going 55MPH on his radar gun.
He was hiding just on the other side of an overpass on a LONG downgrade in the middle of the desert, I'm sure one that people speed down all the time. And then there's Doug, cruising at 55 MPH in his dark windowed Altima watching the trucks pass him by.

Funny how one officer writes that this is a Correctable violation and the other doesn't. All I did was remove the tint, get the tickets 'written off' by my local Police department which cost me $10 per ticket, and then mailed the tickets to the court houses.
In total, this cost me $20 plus two postage stamps and 1/2 hour of my time.

At 200 miles the computer says I'm getting almost 43 miles per gallon which translates to an actual 41 miles per gallon in my car.

At 300 miles I'm still doing a computer projected almost 42 MPG which would translate to a real 39 or 40 MPG average on my road trip.
I decide I've had enough of this crap and pull over to fill up my gas tank again to see what the actual numbers are.

Final numbers:
300 miles driven at an average 53.6 MPH
An actual calculated 40 MPG
After 300 miles, the fuel gage is sitting just below the 1/4 tank mark. That was cool to see.
800 miles IS possible in the Altima. I bet I could do better but I didn't want to break any speed laws and cause any accidents by driving even slower than I did.

No Drafting was done because there was no one going slow enough for me to follow.
No air conditioning was used.
Average junk in the trunk for a 4 or 5 day road trip plus all the other crap I have in there all the time: Long Board, tire chains, piano tuning tools, emergency blankets, first aid, water bottles etc.
Up and down some hills.
I think the overall elevation gain was maybe a thousand feet but I don't remember that one too well.