[en] The successful development of alloys capable of resisting carburisation when exposed to simulated HTR helium relies heavily on a full understanding of the relationships between the minor alloying elements and carbon ingress and on the feed-back of this information to the alloy manufacturers. The purpose of the present report is to further this aim by drawing together in one document several important conclusions and implications arising from the results on sixty commercial, modified and experimental alloys exposed to Oslo Phase IV helium for 2000 hours at temperatures of 800, 900 and 1000°C. At the outset the objective of the study was to investigate quantitatively the empirical relationships which may exist between minor alloy content and carburisation resistance in Oslo Phase IV helium.