Audi's great diesel vehicles--the A3 TDI and Q7 TDI--didn't make the cut for our list (the luxury brand name carries a hefty price premium, though Mercedes-Benz was able to break through that ceiling).

FORBES: Magazine Article

Such a "price-capped cellulosic RFS" approach protects consumers by offering them an effective ceiling while offering investors and producers assurance that all cellulosic fuels produced at these reasonable prices will be mandated.

FORBES: Khosla Speaks

In the euro area consumer-price inflation was revised up to 2.3% in October, well above the 2% ceiling set by the European Central Bank.

ECONOMIST: Overview