Why do suv's burn more gas than cars?

I have a 2000 pontiac grand am. It gets great gas mileage. The epa ratings for it are 20 city/32 highway. It has a 3.4 v6 and it weighs roughly 3100 lbs. I want to get a 97-01 jeep cherokee. It has a 4.0 v6 and weighs roughly 3200 lbs. It has an epa rating of 16 city/21 highway. If they both weigh the same and they... show more I have a 2000 pontiac grand am. It gets great gas mileage. The epa ratings for it are 20 city/32 highway. It has a 3.4 v6 and it weighs roughly 3100 lbs. I want to get a 97-01 jeep cherokee. It has a 4.0 v6 and weighs roughly 3200 lbs. It has an epa rating of 16 city/21 highway. If they both weigh the same and they both have a v6 then why does the cherokee burn considerably more gas?
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