Sorry to post on the Prius forum

I have the same thing on my HCH... matter of fact my first 100 miles on this tank were well over 50mpg... now after 600 total miles it's down to 47. The last 250 miles were at 43 (I reset the 2nd trip meter 200 miles ago).

This is long-term, it happens almost every tank, and I fill up at different times. My driving habits don't really change and the ambient temps have been relatively stable over the last period of time during this tank.

7 - 600-mile tanks... farthest on "normal" gas fill= 643miles

And ONE 735-miler!! (cheated, over-filled tank )