Diesel. Seriously. Thats the answer. Until we run out of oil.
Diesel engines do not need diesel to run. The reason they starting using the fuel we call diesel in these engines was because it was a waste product of gas. So they found a good use for it. Now a days its used so much its in very high demand. We need to invest in the other kinds of fuels that work in a diesel.
Put yes diesel is a good answer.
This will all change with the new bill to get electric cars on the road. Read about the bailout and it's tag on for electric cars. Also the Telsa is a huge step backwards. In the 90s they had SUVs that went further than that per charge.
I don't have the passanger size down, but I do know over in europe they have some say 12 passanger vans that are deisel and they get fairly decent milage for a veichel that size. Even the SUVs can get decent milage, but require money put into them in order to get it. With enoght money invested in after market parts an v-6 explorer (2 wheel drive) can get over 30mpg. The tec is there but there are to many restrictions to be able to do if from the factory.
Now with 4 wheel drive its not going to be as high but still a decent gain. With the v8 (depending on which year) you could get around the same milage and in some cases better milage. Not so much highway or city, but on back roads with a lot of hills the 8 really does help out.
I picked the explore since its a mid sized suv. Once you get bigger then that, well I don't see milage improving to much. The smaller suvs, such as the ford escape can really have their milage improved.
Now what they need to do is get them some deisels and I bet that would really help out SUVS.