Kia's new Rio could have the lowest CO2 emissions of any conventional engined car when it goes on sale in September.

Unveiled to the public at the 2011 Geneva Motor Show, the Rio - a rival for cars such as the Ford Fiesta and vauxhall Corsa - will be available with a new 1.1-litre diesel engine as well as Kia's ISG stop-start system.

Kia is expecting CO2 emissions of 85g/km - lower than diesel versions of the Smart Fortwo and less than hybrids such as the Toyota Prius.

Engineers worked to increase the roominess of the Rio over the outgoing model while keeping weight gain to a minimum. It is longer and wider than before, and has a 70mm longer wheelbase.