Scramjet propelled access to space systems represent a more efficient solution than conventional rockets for accelerating a payload to the velocities required for low earth orbit. Oxygen enrichment is seen as a means by which the upper limit of scramjet performance can be extended in order to increase the viability of scramjets as an alternative access to space system. The following thesis documents an investigation into the Benefits of Oxygen Enrichment for Access to Space Scramjet Trajectories through the use of trajectory simulations. A detailed review of the literature concerning the simulation of vehicle trajectories, the benefits of oxygen enrichment on scramjet performance as well as other relevant fields was performed. The literature review facilitated the development of the structure, from which the current investigation could be launched, as well as the methodology and tools required to complete the investigation. It was identified that a significant amount of work was required to update the current CADAC and supporting dm_cycle trajectory tools, such that they accurately account for the implementation of oxygen enrichment. Additionally, the large number of simulations required, for a thorough investigation, necessitated an efficient interface between CADAC and dm_cycle to be constructed, to which a module named Traj_data.for was developed. The trajectory studies investigate the effect of the enrichment percentage, equivalence ratio and timing of enrichment on the overall performance of three vehicle configurations. The enrichment conditions were manually optimised and trends were drawn to assist with future vehicle optimisations. It was observed that the delayed implementation, of the minimum amount of enrichment required to elevate the combustion efficiency to unity, combined with stoichiometric fuel addition was most beneficial. For the optimised case the enriched vehicle accelerated to Mach 11.17 and 35018m as opposed to the baseline vehicle that achieved Mach 10.79 and 34554m. In light of the experimental setup, this increase in performance is seen to be significant. It was concluded that oxygen enrichment shows much potential as a strategy to increase the performance of scramjet propelled vehicles and it is, therefore, a strategy worth pursuing.