The Automotive X Prize is controversial for its tendency to choose what many perceive not as the most viable or realistic technologies, but the geekiest or most oddball. On the other hand, the innovation and research driven by hopes of winning the $10 million prize could serve to uncover something less than obvious in the hunt for a mass-produced, fuel-efficient and useful vehicle.

Today that prize is a little closer for 43 of the teams in the hunt. Those 43 teams have 53 vehicles entered across the two categories: Mainstream and Alternative. The criteria for advancing to this final stage is that they are the teams most likely to have a real impact on the automotive marketplace with their technologies.

The remaining teams represent six different "fuel" types, including hydrogen, biodiesel, electricity, ethanol, compressed natural gas, and solar power. They also represent some fairly big-name manufacturers.

Among the more recognizable companies remaining in the Progressive Insurance-sponsored X Prize competition are Aptera, Tesla Motors, Tata Motors, Tango and ZAP. Tata Motors is using the competition as a way to help raise its U.S. profile and build brand image and awareness. Tesla, on the other hand, is already fairly well-known for its Roadster and planned Model S sedan, with the latter expected to carry the mantle for this competition. Aptera's 2e three-wheeled vehicle--which recently won Congressional status as a "car"--is perhaps one of the more radical designs.

With just under half of the original 97 teams remaining in the competition, the struggle to find the winners will still be tough. It will take time to sort them out--the final results aren't due until September, 2010.

"Over the next year, we'll see significant advancement of these designs, taking us even closer toward the ultimate goal of making super fuel efficient vehicles a viable choice for consumers," said Progressive CEO Glenn Renwick. To see the full list of remaining teams, hit the link below.