Station wagons do get better mileage than minivans. But there are diesel station wagons available, which increase the wagon mileage. The definition of station wagon is also looser than minivan. For instance, the Kia Soul and Mitsubishi Lance Sport Back are listed as station wagons. Some might consider them hatch backs. And those that get similar mileage are luxury and/or sport models, like the BMW 328i Sports Wagon. The Subaru Outback and Infiniti EX35 might be considered SUVs, yet they are classified as station wagons. The source for this information is fueleconomy.gov. The government doesn’t classify the vehicles; the manufacturers put them into government-defined catagories. But one thing you can be sure of: a minivan will haul more cargo and people than a station wagon ever will. So in that sense, the minivan is a more efficient vehicle.