The car runs on a mixture of stored energy and petrol
Scientists have used wave power technology to build a car that uses half the fuel of a normal city vehicle.
A BMW saloon was converted with equipment to capture energy normally wasted when a driver brakes.
The team from Midlothian-based Artemis Intelligent Power said the equipment was less expensive than the batteries used in existing hybrid vehicles.
Carbon emissions from the prototype were also down by 30% in combined city and motorway driving.
The system, known as Digital Displacement, was originally developed to convert the irregular movements of waves into a steady stream of energy.
A hydraulic drive allows energy usually wasted during braking to be stored and used again when the car needs to accelerate.
The car ran on a mixture of stored energy and petrol, with computer control technology used to switch between the two power sources.
Project leader Dr Wim Rampen said the technology represented a serious step forward in achieving cost-effective fuel economy.
"The system will be much less expensive than electric hybrids and will help to make hybrid vehicles an economic, rather than a lifestyle, choice," he said.
The project was supported by the Department for Transport and the Energy Saving Trust.