My daughter in Europe just leased a Toyota Auris. This car appears to be almost identical to the Toyota Matrix sold in the US. However, the Matrix, with a standard 1.8 liter engine and five speed manual transmission, gets mileage of 26-32. The Auris has a 1.3 liter motor with a 6 speed manual, and gets 33-48 mpg. The Auris also comes in diesel, which gets 45-62 if I have the conversions right. Well the diesel can't pass our smog regulations, but the 1.3 liter/six speed combo ought to be saleable in the US. It looks like the manufacturers still think we are so addicted to power that we would not buy an engine that gets 50% better highway mileage. They may be right. Gasoline pices in the United States now are about a third of what Europeans pay. For most of us, it isn't painful enough yet to fill up.
The Toyota Yaris has an identical nameplate in Europe and the US, but the smallest engine in the US is a 1.5 liter that gets 29 city, 36 highway. The European version comes with a three cylinder, one liter engine that gets 40 city, 54 highway.
Of course, Toyota also makes two smaller models, the Aygo and the iQ, which get even better mileage but couldn't meet US safety standards. Crash test standards are probably a sacred cow, but we really need to give buyers some flexibility to buy a fuel efficient car at a reasonable price.