The continuously regenerating trap (CRT) is a diesel exhaust emission control that removes nearly all diesel particulate matter on a mass basis, but under some circumstances oxidation of sulfur leads to the formation of nanoparticles. The objective of the four year study was to determine CRT performance under controlled, real-world, on-road conditions, and to develop quantitative relationships between fuel and lubrication oil sulfur concentration and particle number exhaust emissions. It was shown that nanoparticle emissions are minimized by the use of ultralow sulfur fuels and specially formulated low sulfur lubrication oil. Nanoparticle emissions increased with higher exhaust temperatures. Fuel and lubrication oil sulfur increased the particle concentration by, on average, 36 × 106 and 0.14 × 10 6 part/cm3 for each 1 ppm increase in sulfur. On the other hand there was a decrease in nanoparticle emissions by the CRT as the system aged.