During three days in September 1991, the Denver University remote sensor (FEAT) was used to measure the CO and HC emissions from 10,000 gasoline passenger cars on a freeway ramp in Goteborg, Sweden. The data have been used to study the emission performance of late-model three-way catalyst (TWC) cars as a function of age and as compared with earlier model years of non-catalyst cars. Regulations requiring the use of TWCs on all new gasoline passenger cars were adopted in Sweden beginning with model year 1989. Due to sales encouragement, a major fraction of model years 1987 and 1988 are also TWC-cars. The results show that the average volume %CO emissions were approximately 90 percent lower for the model years with exclusively TWC-cars compared to the pre-1987 (non-catalyst) model years. The figure deduced from the remote sensing readings for the corresponding reduction of average volume %HC emissions is uncertain due to liquid water occasionally present in the exhaust of some late-model cars, and interfering with the HC measurements. In the high emission region, no major differences in emission performance were observed between model years with exclusively TWC-cars. 16 refs., 10 figs., 1 tab.