Volkswagen Passat
A newly available turbocharged diesel that gets 43 mpg highway accounts for the VW Passat's appearance on the most-improved list. And the Passat TDI can go up to 800 miles between fill-ups. Overall fuel economy in the Passat is up 24% over 2008. Volkswagen Passat

German carmaker Volkswagen AG (ETR: VOW) reported U.S. sales of 37,525 in April, a 38 percent increase compared to the same period last year and the best April for the company since 1971 when VW buses and Beetles (mostly driven by young hippies and unmarried professionals) were ubiquitous.

More than half of VW's gains in April came from Passat and Jetta models.

In addition, Golf/Golf GTI sales rose 14.6 percent the Eos rose 10 percent; Touareg sales climbed 12.2 percent.

The VW CC and Tiguan were the only big losers of the month. CC sedan sales fell 64.1 percent and Tiguan SUV sales dropped 16.4 percent. Sales of the VW Routan, a minivan, fell modestly, by 2.9 percent.

VW sold 13,754 Jetta sedans in April, making the car the company's top seller. VW also sold 1,904 Jetta SportWagens. The company sold 10,096 Passat cars in the model's second month above the 10,000 mark.

An increasing amount of VW's sales have come from high-mileage, clean diesel TDI models. Sales of VW's TDI models rose 35.2 percent from the previous year, making up 21.3 percent of the total. A new Beetle model TDI Clean Diesel Couple will go on sale in summer of 2012.

April was the 14th consecutive month that VW sales outpaced the broader U.S. automobile market, the company noted.