Leading the way: Volkswagen 1-liter Concept -- the world's first 1-liter car uses less than 1 litre per 100 km, 239 mpg. About the weight of a touring motorcycle (290 kg, 639 lb), the 1L seats two, has a single-cylinder 299cc diesel SDI motor, and does 120 kph -- 74 mph. Long, narrow and low-slung, it's a sporty car that's "fun to drive". It was designed in a wind-tunnel, and has the same standards of impact and overturning protection as a GT racing car. VW says it's suitable for everyday use and is "perhaps an indication of a totally new family of cars". The one-cylinder SDI engine has a 6-hole injection jet and pre-injection, two overhead camshafts and three valves, and high-tech lightweight construction, weighing only 38 kg (84 lbs) including the starter-alternator.
http://www.vwvortex.com/news/index_1L.html
http://www.vwvortex.com/news/04_02/04_17/index.shtml

The diesel-powered Volkswagen Lupo 3L TDi is one of the most fuel-efficient cars in the world. It's called the "3L" because its official fuel consumption is below three litres per 100 km -- 94.1 miles per gallon. In 2000 a Lupo 3L went on a globe-trot. It covered 20,699 miles at an average speed of 53.1 mph on daily journeys of between 76 and 478 miles and used only 174.7 gallons of diesel -- an average of 118 miles to the gallon. The best fuel consumption recorded was 141.9 mpg, the worst 100.9 mpg. The Lupo 3L TDi is powered by a 1.2-litre 61bhp three-cylinder diesel engine with direct fuel injection. See "Volkswagen Lupo's record attempt in Australia":
http://www.autoweb.com.au/start_15/showall_/id_VWN/doc_vwg0006011/article.html
"Lupo 3L TDi Back In Wolfsburg":
http://www.diskdrive.co.za/newsstories/vw_lupo3ltdi.html
The Lupo also broke the round-Britain economy record, previously held by a standard Japanese Daihatsu Charade diesel at 103 mpg. Volkswagen engineers are working on a super-economical motor that could go 300 miles on only one gallon of fuel.