Rutting on high quality flexible pavement due to traffic action and is a functional as well as a structural type of failure. That is, it interferes with the quality of ride expected from such a surface and can be determintal to safe vehicle operation. Excessive rutting is an indication that the integrity of one or more of the material layers in the pavement system was not sufficient to withstand the imposed traffic loads. Surface attrition and subgrade deformations also contribute to this type of failure. This report discusses the results of a research study of rutting conducted by the school of civil engineering at Oklahoma State University. This research endeavored to: 1) accurately determine the depth of ruts and the shape of the transverse pavement profile, and 2) detect evidence of the contribution of the bituminous bound materials to this type of failure in heavy-duty asphalt pavement structures. The research did not deal directly with the influence or contribution to rutting of the subgrade soils and non-bitumious base materials. Support for this study was provided by the State of Oklahoma Department of Highways and this support is gratefully acknowledge.