Some say Rwanda is too small to grow enough bio-diesel crops for many buses
Rwanda's first bio-diesel bus has begun its inaugural trip from the capital Kigali to the town of Akanyuru on the border with Burundi.
The Rwanda Biodiesel Express runs entirely on oil plants, animal fats and even used cooking oil from restaurants.
The BBC's Geoffrey Mutagoma, who attended the inauguration, says that it took three years to develop the bus.
The Rwandan government hopes that bio-diesel will help reduce the country's dependence on fossil fuels.
"Using 100% bio-diesel reduces carbon monoxide emissions by 48%," says Jean Baptiste Nduwayezu, head of the Institute of Scientific and Technological Research (IRST).
But researchers estimate that 225,000 hectares of oil plants - such as avocado, moringa and jatropha - would be needed to supply the whole of Rwanda with bio-diesel.
This represents about 8.5% of the country's total area and has led some to doubt whether Rwanda is big enough to make bio-diesel a viable alternative to fossil fuels.
But Rwanda's Minister of Forestry and Mines Christopher Bazivamo dismissed such fears.
"We could plant moringa trees along all the roads. That way there would be no land shortage problem," he told the BBC.