There are plenty of small diesel turbocharged engines moving people around in cars that get 70mpg. Right now these cars are not sold in the US, but that will change. If this happens and they are embraced by people here, you will see an oil glut and another oil price collapse. This technology is well proven and really has been hidden from American consumers.
Hard to do when the US govt is doing its best to make automakers jump through flaming hoops to meet difficult diesel emissions. MPG's have been hurt on 2007+ diesel, volkswagen couldn't even sell diesels in the US last year. Refiners struggle to produce the new fuel and are passing on all the costs to the pumps. Lines are long for diesel cars because few are available.