A prime objective of this research is to related measured moisture changes to soil, climate, and pavement behavior in Oklahoma. Previous interim reports have described operational methodology, procedures for collection and evaluation of field data, and preliminary conclusions of research. After a short historical review, this report discusses relationships obtained after three plus years of data collection at the majority of field test sites and two plus years of data collection at the remaining sites. Evaluation of research data has substantiated several theories of moisture migration and shown several qualitative and definite behavior trends. While relationships described herein are by no means perfectly established, nevertheless it is thought that research emphasis for the remainder of the project should be shifted to the final objective of the study -- development of recommendations for improving highway design and performance in Oklahoma. Some preliminary suggestions are contained in this report and others are currently under more detailed development. This report is the eighth of an interim nature to be submitted by the Subgrade Moisture Variations research project, Oklahoma Research Program Number 64-01-3. Future interim reports will be concerned with recommendations for improving highway performance in Oklahoma