The number of new private cars licensed fell 39.8 per cent during May, the fourth consecutive month that the figures have fallen year on year.
According to the Central Statistics Office, there were 12,172 new private cars registered for the first time in May 2008, compared to 20,232 in the same month in 2007.
Meanwhile, first licensing of second-hand private cars fell by 8.4 per cent, and new good vehicles also slipped, falling 32.7 per cent to 3,219 compared to 4,780 in May 2007.
Overall, the number of vehicles licensed during the month was down almost 30 per cent compared with the same period a year earlier.
The decline may be attributed in part to the new vehicle taxation system that is due to come into effect on July 1st. Under the new regime, those vehicles with lower emissions will pay less in tax, while those with higher emissions will see an increase in levies.
The number of petrol cars registered during the month still exceeded diesel, with 8,410 petrol cars licenced compared to 3,300 diesel. Some 388 petrol and ethanol cars were registered during the month, along with 73 petrol and electric cars.
This brings to 2,039 the number of petrol and ethanol cars registered in Ireland up to the end of May, and 788 petrol and electric private vehicles.