A methodology has been developed for making continuous, high-precision measurements of atmospheric oxygen concentrations by modifying a commercially available paramagnetic oxygen analyzer. Incorporating several design improvements, an effective precision of 0.2ppmO2 from repeated measurements over a 1-hour interval was achieved. This is sufficient to detect background changes in atmospheric O2 to a level that constrains various aspects of the global carbon cycle. The analyzer was used to measure atmospheric O2 in a semicontinuous fashion from air sampled from the end of Scripps Pier, La Jolla, California, and data from a 1-week period in August 1996 are shown. The data exhibit strongly anticorrelated changes in O2 and CO2 caused by local or regional combustion of fossil fuels. During periods of steady background CO2 concentrations, however, we see additional variability in O2 concentrations, clearly not due to local combustion and presumably due to oceanic sources or sinks of O2. This variability suggests that in contrast to CO2, higher O2 sampling rates, such as those provided by continuous measurement programs, may be necessary to define an atmospheric O2 background and thus aid in validating and interpreting other O2 data from flask sampling programs. Our results have also demonstrated that this paramagnetic analyzer and gas handling design is well suited for making continuous measurements of atmospheric O2 and is suitable for placement at remote background air monitoring sites. ¿ 1999 American Geophysical Union