A. The European driving cycle is different than the US EPA driving cycle. The numbers are not comparable. The euro cycle results in lower number. B. The 2.5L I-5 in the Golf doesn't get 30mpg. It gets 30 mpg HWY, but 25 on the combined cycle, which is what is generally quoted unless they say HWY. The Golf has fairly poor fuel economy for the sector. The ford focus gets 28 combined. The cobalt gets 30mpg combined (all numbers for manuals), which is worth bragging about because it is the best non-hybrid fuel economy in the US. C. American drive bigger cars. We drive a lot more miles that Europeans do in longer trips. We're not alone in this, look at other big countries. Australia's best selling car is the Holden commodore. This is a big ass car. As big as a BMW 7-series. It was sold in the US as the Pontiac G8 and got 20 on the combined cycle. D. Diesels are not popular in the US. This is because diesels are quite dirty and pump out particulate emissions that can have more worrying consequences than CO(2). Most diesels (and many other cars in Europe, where cars without catalytic converters were sold well into the 90s) fail US emissions test spectacularly, hence they are not sold here. The only car diesels that pass US emissions are the urea injected models (VW Jetta TDI, BMW 335d, Mercedes E320 Bluetech) sold here in limited quantity. They are complex and expensive. There are other reasons for not using diesel. An amount of diesel's economy is contained in the fact that it contains more energy in it. This doesn't appear magically, it requires more oil to make a gallon of diesel than a gallon of gasoline. Diesel is cheap in europe because it is not taxed as heavily, it is often more expensive in the US than gasoline. It is also worth noting that refineries can't just produce diesel or gasoline. They are basically byproducts of each other's production. Anyone remember the fuel crunch a few years back? It hit Europe much worse than the US. This is because the crunch was in refinery capacity. All of Europe's diesel was spoken for in its fleet. All of the US's diesel was as well (due to out trucking fleet). However, Europe did not use as much gasoline as it produced, allowing us to import large amounts of gasoline from Europe, lowering US gasoline prices. There is something to be said for energy diversity. Finally, the US is a leader in alternative fueled vehicles. Bio-diesel is in wide distribution here for use by commercial fleets. California (particularly West Sacramento for some strange reason) is the center of fuel cell development. While these cars often have foreign branding, the technology was purchased from researchers in CA. Tesla, the most well known of electric car makers, is based in the South Bay. There are also a wide array of less well known companies making streetable electric cars. Ford's hybrid technology is better than Hondas and equal to Toyota's. The Chevy Volt is going to be a huge leap forward and knock Toyota on its ass.