Despite many decades of study, models of discharges in molecular gases still lack accurate data on many key col-lisional processes, both in the gas phase and on surfaces, necessary for reliable predictive modeling. Good data is lacking for electron-impact dissociation, surface recom-bination, reactions with metastables, gas heating mecha-nisms, energy transfer, and surface thermal accommoda-tion. This is true even for such “simple” and ubiquitous gases as O2 and N2. Diagnostic techniques have advanced significantly, with an emphasis on accurate absolute den-sity measurements, space and time resolution, and energy distribution functions (translational, rotational and vibra-tional). However, most studies focus on measuring only a few of the modeled parameters for a given system, and often in plasma configurations optimized for applications rather than for model/experiment comparison. Particularly problematic is the presence of large gradients (in temper-ature, density, composition) as well as poorly-controlled surface conditions. Our approach therefore is to use a well-characterized, stable and uniform discharge chosen to be simple to model, namely a DC positive column in pure O2, and to perform a comprehensive set of measure-ments of all accessible parameters using multiple (and sometimes overlapping) diagnostics. The mod-el/experiment comparison is therefore highly constrained, allowing the origin of discrepancies to be probed in un-precedented detail.