The results of a study conducted to determine a new binder parameter that might replace the existing Superpave high-temperature specification parameter (G*/sin delta) are described. The current parameter (G*/sin delta) is inadequate because of increasing concerns about its applicability to polymer and other modified asphalt binders. In this study, several parameters were calculated from rheological test data generated on four asphalt binders of different grades at four test temperatures. Two of the binders were unmodified binders, and the other two were modified binders. Laboratory hot-mix rutting tests also were conducted at three temperatures on the asphalt pavement analyzer (APA) and the dry Hamburg rut testers. APA overestimated the rutting potential of modified binders used in this study. Dry Hamburg produced reasonable results. From the correlation between the dry Hamburg data and binder parameters, the storage viscosity, eta', was found to be the most promising binder parameter that could adequately characterize the rutting resistance of both unmodified and modified asphalt binders. Of all of the parameters, it was the easiest to measure with minimal change in existing instrumentation and software. A specification criterion for eta' was determined. According to the new criterion, the temperature at which the eta' has a value of 220 Pa-s for rolling thin film oven-aged asphalt binders is the high-performance grade (PG grade) temperature that may reasonably replace the current Superpave high-PG grade temperature obtained using G*/sin delta.