Toyota's claim that the Japanese-market version of its third-generation Prius petrol-electric hybrid vehicle has achieved the world's best fuel efficiency for a mass-produced vehicle has raised a few eyebrows.

Toyota says that the Prius produced a stunning 38km/L fuel economy number. This, in our language is a remarkable 2.6L/100km.

However, this incredible economy was achieved using the regular Japanese 10-15 test cycle of the Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT).

Though a kosher value in Japan, the 10-15 low speed and low acceleration mode drive cycle bears no relationship to the tougher US EPA city drive cycle used in our benchmark Australian Design Rule 81/02.

While it's reasonable to expect that the new Prius will be a very thrifty sucker, and maybe with world beating economy figures, we'll wait until we see an ADR-related number before we organise the bubbly, the brass band and the marching girls.