The new Toyota Prius will average 72mpg and emit 89g/km of carbon dioxide.
Toyota revealed the all-important economy figures for the European specification Prius ahead of tomorrow's Geneva motor show.
The figures compare to the current model's average of 65.7mpg and emissions of 104g/km, and will make it officially the cleanest mass-produced car on sale.
The fuel savings of up to 14% come despite a power increase of 22%, helped by the switch from a 1.5- to 1.8-litre petrol engine.
To incorporate the larger engine, Toyota has focussed on weight savings and better packaging of the hybrid system, which is lighter and smaller than the current unit.
Further weight-savings have been achieved through the use of lightweight aluminium and high-tensile steel to build the car.
Toyota also says the new Prius's platform provides better handling, stability and safety.
The bodywork has also been tested in a wind tunnel to provide the least drag of any mass-produced car on sale.
In particular, attention has been paid to airflow beneath the car, to reduce running noise, improve stability and increase fuel efficiency.
The new Prius is slightly longer than the current model, while the roofline has been altered to improve rear-seat headroom. The repackaged hybrid system also allows for a larger boot.
The new Toyota Prius will go on sale in the UK in July, and will fight for sales with the new Honda Insight.
No prices have been released for the Prius, but it is expected to cost around 18,000, 3000 more than the Insight.
However, the Insight falls short of the Prius's vital statistics with an average of 61.4mpg and CO2 emissions of 105g/km.