I purchased a 2007 Nissan Altima last year to replace our 2003 Ford Windstar. Primarily this was done because we put on a lot of miles each year and fuel costs were rising. The Altima ratings were 6.3l/100km or 45 mpg on the highway. They were 8.9l/100km or 32mpg in the city.
The only one (rating), that has proven to be true of the EPA ratings posted on the vehicle, is the city driving one. My car now has 32,000 km`s on it, so it is definitely "broken in".
I have just returned from a trip to Thunder Bay, ON from Ponoka, AB. I kept track of all fuel used. With 2 adults and 2 children and our luggage, at 115-120km/hr in Alberta the car returned 36.68mpg. At 112km/hr it returned 34.55mpg on more than one tank. At 102km/hr in Ontario, it returned 34.68mpg on the way down and 36.82mpg on the way back. Cruise control was used for the entire trip.
Nissan had asked me to track the performance, after I complained about the incorrect economy rating. Most of this driving was done on divided highway, so there was no passing of other vehicles involved. The highway ratings for this vehicle were based on a 16 minute trip with a top speed of 90km/hr and a low speed of 62km/hr with an average of 77km/hr. The car is never even actually on the road! This is done on a platform with only the front wheels turning! Is this to be considered an accurate fuel economy test? I think not.
Well I just got myself an 08 Altima SL, to date my mileage is 38 mpg combined, I think this excellent and needless to say I'm tickled pink with this purchased. BTW my speeds are 90kmh secondary roads and 115kmh divided highways + the villages and the city.