Diesel engines are more fuel efficient than gas engines. 

 For example the RAM 1500 has an

 EPA estimate of 21mpg on the city and

 29mpg on the highway while the 30-liter EcoDiesel V6 

 has 17 compared to the city and

the Pentastar® V6 36-liter

 at 25mpg for the RAM 1500.

at 25mpg for the RAM 1500.

 On the road