The share of diesel vehicles among new car registrations in the EU decreased from a peak of 55% in 2011 to 49% in 2016. Recent data indicate that diesel shares continued to fall in 2017 and early 2018. Because diesel technology was thought to have a key role in the EU's overall strategy for reducing CO2 emissions from passenger vehicles—diesel engines historically possessed a number of efficiency advantages over gasoline engines, and diesel vehicles generally consume less fuel than comparable gasoline vehicles, though for various reasons CO2 emissions from diesel engines are not lower in the same proportion—the question arises whether this trend will affect Europe's ability to meet its climate targets. This briefing summarizes the reasons why diesel's decline does not put EU CO2 targets out of reach. As demand for diesel passenger cars in Europe wanes, manufacturers have numerous lower-cost pathways to meet the EU CO2 targets. In terms of efficiency, gasoline engines have gained ground against diesel engines thanks to a suite of efficiency technologies, a trend that will continue, and the growth of competing technologies—hybrids and electric vehicles—further changes the picture. In summary, a decline in diesel shares down to 15% in 2025 would not interfere with meeting EU CO2 standards and would actually decrease costs of meeting CO2 standards.