The Toyota Prius Prime is an outlier when it comes to cars that happen to top our monthly plug-in sales scorecard. This is because - aside from the Chevrolet Volt and BMW 530e - our top seven best-sellers are BEVs. The only other PHEV on our top 10 list is the Ford Fusion Energi. However, Volt, Energi, and 5 Series plug-in sales pale in comparison to the Prime. In the U.S., Toyota has delivered an impressive 18,310 Primes on the year through August 2018.