The Toyota Prius C, the Japanese brand's new city-sized hybrid, will not be significantly more fuel efficient than the larger regular Prius, if at all.

Prius c - Aqua in Japan(Overseas model shown)

Toyota Australia this week revealed it expects the new Prius C to have a city (urban) fuel consumption rating of about 3.7 litres per 100km.

This is lower than the Prius's 3.9L/100km city figure and will officially make the Prius C the most fuel-efficient combustion-engined car to drive in the cities when it makes its local debut in March/April.

Toyota has yet to reveal the Prius C's combined figure.

The model's combined consumption figure was also expected to be lower than the Prius's 3.9L/100km that takes into account both urban (city) and extra urban (suburban essentially) results according to Australian fuel consumption cycle tests, though Toyota insiders have indicated to CarAdvice that the figure will be much closer based on Australia tests.

Our sources say that while the Prius C is lighter and smaller than the Prius, because it is powered by a smaller engine that inevitably has to work harder at faster speeds - such as freeway driving and for the Extra Urban test that runs cars (also on a laboratory rolling road) at up to 75km/h rather than the maximum 50km/h of the Urban test.

The Prius C has a combined power output of 74kW from its 1.5-litre 'Atkinson Cycle' four-cylinder petrol engine and electric motor. The normal Prius generates 100kW from its bigger, 1.8-litre engine and electric motor.

The Ford Fiesta Econetic would retain its status as Australia's most fuel efficient car, with a combined figure of 3.6L/100km, followed by the 3.8L/100km of the Mini Cooper D hatchback.

Both the Fiesta Econetic and Cooper D are diesel-powered vehicles, however, which would at least allow Toyota to claim it has the more environmentally friendly city-sized hatchback on the market.

The diesel hatchbacks have relatively low air pollution ratings compared to petrol-powered rivals.

Toyota Australia has yet to confirm pricing for the Prius C - called Aqua in the Japanese market - which could potentially undercut the country's current most affordable hybrid - the $29,990 Honda Insight.

Toyota will also launch a bigger version of the Prius, called the Prius V, in the second quarter of 2012.