The U.S. Environmental Protection Agency (EPA) Building Assessment Survey and Evaluation (BASE) study included a range of measurements in 100 randomly selected U.S. office buildings for the purpose of characterizing the existing building stock with respect to determinants of indoor air quality and occupant perceptions of indoor environments. One aspect of the evaluation was the characterization of the ventilation systems serving the study spaces and selected measurements of ventilation performance. This report presents an analysis of these data with a focus on supply and outdoor airflows, including comparisons of the measured data with design values and the outdoor air requirements in ASHRAE Standard 62-2001. The results indicate that, as expected based on thermal load considerations, the average value of the design and measured supply airflow are both about 5 L/sm2 (1 cfm/ft2). The measured outdoor air ventilation is higher than might be expected, with a mean value of 49 L/s (105 cfm) per person based on volumetric airflow measurements at the air handlers and measured occupant densities. These outdoor air ventilation values are high on average relative to the minimum outdoor air requirements in Standard 62 due to the high outdoor air fractions (relative to minimum) and the actual occupancy being on average 80 % of the design occupancy. Nevertheless, about 17 % of the ventilation measurements are still below the 10 L/s (20 cfm) per person requirement in Standard 62. Under conditions of minimum outdoor air intake and accounting for the lower occupancy levels, the mean ventilation rate is roughly 11 L/s (22 cfm) per person and about onehalf of the values are below the per person requirement in Standard 62. In addition, this report contains a number of suggested modifications to the protocol used in these assessments for consideration in future studies. This report is a revision of the original report on these data published in 2004. This revision reflects some additional analyses of the data, which results in some changes to the numerical values reported, but not to the overall conclusions.