To find out, they pitted a hybrid, a diesel, a compact and a really tiny mini-compact against one another on a road trip from Los Angeles to Las Vegas.
They put the cars through three real-world driving tests along the way:
They then combined the results of those tests to determine the overall winner.
The cars they selected were the Ford Focus, the Smart ForTwo, the Toyota Prius (all 2008 models) and a 2005 Volkswagen Jetta TDI. In the end, one car really was the real fuel economy king.