Did an experiment on Sunday on a trip. Ran 41 EV miles to bring EV to 0 and then turned on HV charge. Charged as much as it allows. 68.5 miles in HV Charge mode @ 65-70 mph. Added back to 20.4 EV range. So gained about 0.3 miles EV per mile driven in HV charge. Ran some EV miles and some more HV charge. In all ran 108.2 HV charge miles on the way there. FIlled with 3.022 gal. Drove HV on the way back home. Turned out to be 108.7 coming home. (We didn't start the trip from home so that explains the miles difference on the trip halves.) Filled with 2.912 gal. So HV Charge was 87.8 miles / 3.022 gal = 29.05 mpg - BUT - that added 20.4 miles range. If I add those miles in it is 108.2 miles / 3.022 gal = 35.80 mpg. HV was 108.7 / 2.912 = 37.33 mpg. So not a lot of difference. Very little elevation change in West and Mid Michigan - 100 ft difference between start and mom's house. Light tailwind of 5 mph on the way home. FWIW - When we switched to HV Charge I expected the tenths of miles of EV range to start climbing. They didn't. We drove for a while with the EV range showing a steady 0 until it had added enough to add a bar the the EV range indicator at which point the EV range jumped from 0 to 1.9. After that the tenths started incrementing.