Be Careful of Upgrades — Car rental companies sometimes offer free upgrades to larger vehicles in order to save the more fuel-efficient vehicles for specific requests from those aiming to save money on gas. Larger vehicles will cost you more in fuel costs.
I often get upgraded to a Mercury Grand Marquis (I feel like I’m driving a car my grandparents would have driven) or a mini-van. Last week the car rental agent was so excited because I agreed to take a mini-van. She was bragging to the other agents that she was successful in sending this mini-van out the door.
If you want to save money on fuel, decline the upgrade … because in this case something better can be deceiving.