How much ethonal depends on the time of year, where you live and the brand of gas.
Whenever I use Shell or BP I get better mpg than if I use Speedway which is a discount gas station.
They are required by law to post on the pump how much ethonal they put in their gas.
Places like CA use it in all their gas all the time, places like MI use it in the winter time to prevent gas line freezing.

 

Depends on where you are, and also what time of year. Eastern PA has 10 or 15% added between about November and February (forget exactly when - there is a sticker on all of the pumps). Everything takes a noticeable MPG nose dive, and many people with 8s end up having to go up a grade to keep from pinging under load.

 

Spikes right I have a choice to fill up in CA or NV so I try to always fill up in NV. Our house is at 6400-ft which sucks the power out of any engine. All the Pa/Ma Kettle driving advice on road and the drag issues are anyones best bet for mpg. I took my disco over a pass and down to 5200-ft, the roof rack which was already mentioned earlier in this thread is a drag monster! I had to give her gas all the way down the mountain with the sail on the roof !! Barring a camping trip that's coming off the roof asap.

 

The ethonal is used in areas that have a Federal mandate to reduce emissions.
10% is what the standard is.
In the winter there places that have high emissions so ethanol is used, before it MTB's.
In Dallas TX we are forced to use 10% ethanol year round, So mileage takes a hit most times it more than the ethanol displaces so you burn gas to burn the ethanol,

 

I'm like you slowly working on the maintainence and gas milage. I put some marvel mystery oil in the gas to see if I could free up a sticky lifter and it seems to have helped the gas milage. I took it offroad twice about a total of 2 hours and got 13.5 or so I was getting before. so I'll keep it on the road and see if I have an improvement. I put it in heavy to like 12-16 oz. to the tank of gas.

 

Everyone of us has posted EXCELLENT ideas on MPG, but lets be honest the fact that the Disco wasn't going to get great MPG was in my top 5 list of things I had on my mind when I hunted the X Mas Tree down on C.L. The best solution is to strap on some jerry cans and hit the trails responsibly.