Three methods for rejection of CO2 data were used to obtain CO2 concentration versus time for 1968--1973 for Station Charlie (a ship in the North Atlantic), Niwot Ridge near Nederland, Colorado, and Key Biscayne near Miami, Florida. From examination of the results it was concluded that short-term variation and error were not large for the Station Charlie data. There was a suggestion of occasional contamination at Key Biscayne and evidence of more frequent contamination at Niwot Ridge, after 1970. Values obtained for annual CO2 increases were 1.3 and 1.2 ppm (1959 SIO index) for Station Charlie and Niwot Ridge. Annual amplitudes were 15, 11, and 9.7 ppm for Station Charlie, Niwot Ridge, and Key Biscayne, respectively.