If I had to make a wild guess, I'd say it's just due to A/C use, really. I mean, I can get anywhere from 35mpg on a bad drive home from work with the A/C blasting to 45mpg or even twice now I've gotten over 50mpg with no A/C use and optimal driving conditions. This is of course with my own Civic HX, Honda's other lean-burn Civic. Maybe we should have a Phoenix meet some time to share techniques and such? Also I'd love to hook up my ScanGauge to a Civic Hybrid and compare a few things from the hybrid to my non-hybrid Civic.