All of your fuel-ups so far have been marked as partial. When you enter a partial fuel-up, you don't get an individual MPG value for that particular fuel-up or the next one. Fuelly uses a method of calculation that relies on finding the difference from full each time you fuel-up. If Fuelly doesn't ever get a full tank to work with, you won't get a running MPG value. Here's more info about filling all the way up.