sometimes
Cars don't get better gas or mileage.
The general improvement for 2012 cars is better gas mileage. All 2012 cars seem to have that feature.
Better gas mileage.
The best gas mileage from unleaded gasoline or premium gasoline depends on the car. Old cars get better mileage from unleaded.
Newer cars are geared towards being more fuel efficient than older cars. Cars made in 2012, depending on engine size, will likely get much better gas mileage than your 1993 Buick. These older cars were geared more towards comfort and power and less towards improved gas mileage.
Cars don't get better gas or mileage.
Bicycles give you more gas mileage.
A smaller car with 3 or 4 cylinders usually gets the best gas mileage. Also, hybrid cars tend to get better mileage on the city streets than regular cars because of their regenerative braking.
It obviously depends on the cars being compared but generally Diesel provides better gas mileage.
Because gas prices are going up...
Most are diesel powered stick shift models that are smaller and lighter than American cars.