This study examines the relationships between regional ozone (O3) pollution and emissions of nitrogen oxides (NOx) in the eastern United States during summer. Using measurements from rural sites during the summer of 1995, three 4-day time periods are identified during which significant enhancements of surface O3 occurred on spatial scales ranging from 0.5 to 1.8 million km2. Each of these episodes was characterized by relatively stagnant meteorological conditions conducive to the photochemical formation and accumulation of O3 in the boundary layer. The surface ozone accumulation efficiency (SOAE), a parameter which relates the O3 accumulation to the NOx emission density in a given region, is estimated to range from 1 to 2 ppbv O3 kg-1 N km-2 in the eastern United States during summer. This result is discussed in the context of regional NOx-based O3 control strategies. In addition, the net ozone production efficiency (OPE) is estimated to range from 2 to 3 ppbv O3 ppbv-1NOx in this region. ¿ 1998 American Geophysical Union