PriusChat's own TheForce just finished up an astounding 2502 mile, 299 MPG tank of gas in his 2006 Hymotion PHEV Prius. Here is the post from TheForce:
Yes a PHEV does work and it works very well despite what fleets or car reviewers say!
I just filled up today with 2501.7 Miles and 299.43MPG on one tank of gas and I still had gas left over for 500+ more miles.
This tank started on March 28th 2009 and ended today July 14th 2009. It ended because I'm heading up to Hybridfest and I wanted to start with a fresh tank. This tank was mostly my commute to work and back. About a month ago I moved into a new house which my commute distance did not change much but I gained much better low speed near level roads. With these new conditions I believe I can achieve 4k even 5k miles now on one tank of gas.
My new routine is as follows. I start out on 35mph roads in EV mode. I take a back road which is 25mph to the highway. Once I get on the on ramp I exit out of EV mode to let the engine warm up though S1. By the time I get through S1 I enter into the city and go into EV mode all the way to work. On my way home I do the opposite. I EV all the way to the highway. Once I enter the 55mph zone I go through S1 and by the time I get off the exit to the 35mph roads I can get into EV mode. Then its EV all the way home. According to my ScanGauge this totals out to about 400-500MPG per trip.
So here is the data you have been waiting for.
Distance: 2501.7 miles
Calculated MPG: 299.43MPG
Gallons gas used: 8.355 @ $2.599
Watt hours used: 439556.7 @ 8 cents per kWh
Watt hours per mile: 175.7
Total tank cost: $56.88
Cents per mile: 2.3
Here are some pictures.
ScanGauge reporting not very accurate.

Since I had to reset my CAN-View here is the last 323 miles. The CV tops out at 255MPG so I set it over to L/100km to get a better reading. The CV is worse than the SG reading. There is so little fuel used its hard to get accurate numbers.










