This paper presents the development of the concept of emission testing on a mass basis and the establishment of emission baselines and standards. Data from tests run on several fleets to establish equivalency factors between average exhaust emissions when testing according to the 1970 (7-mode), 1972 (CVS-C), and the 1975 (CVS-CH) federal test procedures are listed. These data were used to establish the 1972, 1973-1974, 1975, and 1976 standard values.Tests were run on 30 precontrol vehicles by both the 7-mode and CVS-C procedures to derive the factors used to translate the 7-mode procedure baseline data into equivalent CVS-C procedure baseline data for precontrol vehicles. These values were used to establish the 1972-1974 hydrocarbon (HC) and carbon monoxide (CO) light-duty vehicle standards.Similar tests were run on 138 1970 vehicles to establish standards for the CVS-C procedure that were equivalent to the 1970 standards using the 7-mode procedure. Tests were also conducted on 90 vehicles to derive factors relating emissions from the CVS-C and CVS-CH test procedures. The results of these two programs were used to establish the 1975 HC and CO standards.A baseline study was run on 245 1971 vehicles to determine the average oxides of nitrogen (NOx) emission level for 1971 vehicles when testing according to the CVS-C procedure. These results were used to establish the 1973-1974 and 1976 NOx standard values.The 1975 NOx standard is equivalent to the 1973 standard. The NOx emission factor from the 90-vehicle fleet program to relate the CVS-C and CVS-CH procedures was used to derive the 1975 NOx standard.The paper includes the test data and a discussion of the rationale behind the derivation of the standards.