The study and design of light-weight automobiles has emerged as an important area of interest in the government, academia, and the manufacturing industry. Significant advances in vehicle weight reduction technologies have taken place in almost all fields of transportation. Weight reduction is identified as a key factor to achieving fuel-economy, energy efficiency and environmental safety. The main objective of this thesis is to investigate cost effective design methodologies that enable fabrication of light weight structures, which subsequently result in a fuel saving. A few important techniques and trends of weight reduction in the automotive industry over the past few years are studied as part of the thesis. A summary from the survey of various approaches to weight reduction is presented in the literature review. This thesis is based on the theory of semi-tension fields, which was originally applied towards the design of structures in the aircraft industry. A semi-tension field is a post buckling phenomenon in which the load is continued to be carried even after the web has buckled. The advantage of semi-tension fields is twoold: first, by using this theory the structural stability of the original structure is retained; and secondly, its application replaces a comparatively heavy-weight shear resistant web with a thin web, potentially resulting in reduced weight. The semi-tension field theory is applied to the redesign of back panel of a prototype Ford F-150 pick up truck, which was modeled and analyzed using IDEAS Master Series 8 FEA software. The literature review also consists of the survey of several advances in the Semi-tension fields theory, and the corresponding trends in weight reduction. Analytical theories related to semi-tension field-based design and the respective mathematical formulations have also been described. Finite element analyses of the design that resulted from the application of the theory were carried out and results were validated using analytical theories. A technical paper demonstrating the redesign of a door beam was also studied and results are presented as an appendix.