Up to 70% of new cars sold in Ireland so far this year have been diesel, according to the Central Statistics Office.
CSO figures show more than 22,000 new private cars were licensed in July, an increase of 5.5% compared with July 2015.
For the first seven months of 2016, 119,952 new private cars were licensed, a rise of 20% on the same period last year.
Hyundai was the most popular make of new car sold last month, followed by Ford, Toyota and Nissan.
5,600 used cars were licensed in July - a 38% rise on the same month last year.