The average mileage of both city and highway use that I am getting on my Swift diesel is 24 kmpl. Most of my driving is around the city with light to medium traffic conditions. The thing that you have to keep in mind is that while you are driving, you should keep the rpm of the engine constant and try to drive in a higher gear. Use an engine oil that assures you a better quality and avoid sudden braking at traffic lights and slow down your car beforehand.