Driving the ML350 Bluehybrid in "S" mode, with the stepped gear shifts, it felt pretty much like any other M-class, especially since the cold weather was forcing the engine to remain on for more of the time. Pussyfooting around in "E" mode, I did manage some fully electric operation, but never to 34 mph (during my half-hour of city driving in the vehicle, the battery state of charge graphic never showed very far above half full and the fuel economy on the trip computer read 21.8 mpg). EPA certification isn't complete yet, but given that the Chevy and Dodge units managed to boost city fuel economy by 36-40 percent, let's assume the high end of M-B's target range (30 percent) for city. Highway goes up only five percent on Chevy, zero on Dodge, so let's guess maybe 1 mpg there, bringing our fearless prediction to 20/21 mpg city/highway. (Remember, your mileage may vary!)

Drivability on this prototype, which is still undergoing development changes, felt impressively smooth. The engine fired seamlessly, the brake actuation was completely linear, with no noticeable handoff between regenerative and hydraulic retardation. The one area in which there may be room for improvement: the hybrid system graphics are totally "last-generation." Just a simple power-flow diagram indicating battery charge level, and a bar-chart fuel-economy graphic (that also shows the amount of energy regenerated each period as green bars below the zero line). We've tasted the 2010 Ford Fusion interface, and its EV-threshold notification, accessory load graphics, etc. have established a new benchmark.

There's no word yet on pricing, but converting an engine with variable valve timing to run the Atkinson cycle shouldn't cost any more than introducing cylinder-shutoff to a single-cam pushrod engine, so perhaps the roughly $3500-$3600 Chevy and Dodge charge is a good estimate. In any case, expect the ML350 Bluehybrid to price out between the ML320 Bluetec diesel and ML550 V-8.