Fuel cell vehicles are powered by electricity generated in the chemical reaction between the hydrogen used as fuel and oxygen in the air, producing only water as by-product and none of the gases such as carbon dioxide that are blamed for global warming.

But for such vehicles, the amount of emissions is quite large if the processes of exploiting primary natural resources and turning them into fuel are counted, nearly matching the amount of overall emissions from hybrid cars, the study pointed out.

The study, conducted by Toyota Motor Corp. and the Mizuho Information & Research Institute, estimated the amount of gases on a "well-to-wheel" basis, which counts emissions from processes ranging from energy exploitation and fuel production to consumption.

Discharges of gases from hybrid cars are less than half the amount of gases from vehicles solely powered by gasoline engines, the study said.

The study is Japan's first comprehensive estimate on the amount of vehicle-related emissions of greenhouse gases, according to Toyota and Mizuho Information. Its full report will be presented to a convention of the Japan Society of Energy and Resources on Jan. 27.