This study, a meta-analysis of PEMS data from EU (Euro 6) and US (Tier 2 Bin 5/ULEV II) diesel passenger cars, documents the wide discrepancy that exists between official certification or type-approval emissions of nitrogen oxides (NOx) from new diesel passenger cars and actual NOX emissions from those vehicles during real-world, everyday operation. The study comes on the heels of a recent report showing that a similar gap between official and real-world emissions of CO2 from passenger cars in Europe widened to 38% in 2013—i.e., CO2 emissions (and fuel consumption) during everyday operation were on average more than a third higher than the certification values obtained for vehicles via laboratory type-approval test.