Well since they are very similar cars in very similar conditions your only variables are:

Highway vs City
and
Driving style (how aggressive you are with the throttle and how much time you sit around idling compared to him)

You should also realize that some cars may set off the low fuel light much earlier than others... even of the same year and model. Many cars these days 'learn' where their limits are. For example my silverado had a 26 gallon tank and used to tell me "Low Fuel" when I still had 10 gallons left! Eventually after it 'learned' that I was quite a ways away from running out of gas it started warning me closer to when I really was low.

Accords may do the same thing, and his Accord may just have 'learned' its limits already while yours hasn't.

Don't compare you cars as to when the low fuel light comes out.

A much better way of comparing fuel economy is to

Step 1- go fill up completely today and reset your trip meter
Step 2- Drive around like you normally do
Step 3- whenever you are getting low (doesn't really matter when) go fill up
Step 4- Take the number of miles on your trip meter and divide the number of gallons you just put into it... then tell him to do the same and compare your MPG.



And BTW, yeah the pic in your sig looks very photoshopped.