This research investigates the oxidation behaviour of an additively manufactured (AM) superalloy Inconel 718 and compares its oxidation performance to that of wrought Inconel 718. A plasma arc additive manufacturing process was developed and utilized to manufacture the AM specimens. All specimens were subjected to exposures at 800°C and 900°C. The oxidized specimens were analysed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Both surface oxide and cross-section microstructure were examined, in addition to microstructure changes in the substrate. The results showed that the two alloys had similar weight changes over the periods of 50-400 hours at both temperatures. However, the microstructure changes on the surface and in the substrate were different. The thickness of the chromia oxide scale formed on AM Inconel 718 was consistently thinner than that on the wrought specimens. There was also more internal oxidation on the AM specimens, particularly after longer exposure at high temperature. In addition, the formation of a subscale Nb-rich layer was observed between outer chromia and substrate on all specimens, except on the AM specimens exposed to 800°C for 100 hours, this layer contributed to the integrity of the chromia oxide layer. Based on the preliminary results, it was concluded that the AM material, when exposed to 900°C, had slightly inferior oxidation performance than the wrought alloy, attributable a thicker and more stable chromia oxide layer and to less internal oxidation. I would like to thank Carleton University and the Department of Mechanical Engineering for giving me the opportunity to perform this research I want to thank my advisor, Dr. Xiao Huang, for her support, insight, patience and encouragement during this process. I would like to thank all of my friends and family members for their continued support and cheering me on when things were tough. I would like to thank my parents, Mario and Roxana, and my fiancé Eduardo for being a constant source of love and encouragement, and never letting me give up. Lastly, to my dear sister. You are awesome and you are the best.