We have two cars for two drivers. It would probably take more gas for us to have just one car than for us to use two cars.
First, we would have the pain of getting two cranky children up and ready for the day to leave the house a 6 a.m. and then we'd have to drive Dad to work about 20 miles away. Since nothing is really open so early, we'd have to drive all the way back home (drive total of 40 miles). Then, DS would need to go to preschool 10 miles away, I would run a few errands and head home with DD (we're now up to a drive total of 60 miles). Then, we'd have to go get DS from school in the afternoon (our total for the day is now 80 miles). Then, DD had better nap quick because we wouldn't have more that a few hours before we'd have to go get DH. So, that would be a total for the day of 120 miles of driving on one car. And I and the kids woud be very cranky.
Currently, driving two cars, DH drives 40 miles a day to/from work. And I drive 40 miles taking DS to and picking him up from school and running my errands. So, that's a total of 80 miles of driving each day.
We have a Subaru Forrester and Toyota Corolla. Both get pretty good gas mileage, but the Corolla is slightly better because it isn't AWD and it's smaller than the Forrester. When gas prices got so high last year, we tended to bundle our errands into fewer trips to town and we took the Corolla out for our weekend errands (we usually take the Subaru because it has more room with the kids).