In early 2012 a metallurgical investigation was performed on a section of pipe from a crude oil pipeline that leaked in service. The pipeline is located in Northwestern Canada. The investigation concluded that internal stress corrosion cracking (I-SCC) was the primary mechanism by which a crack could have initiated and propagated nearly through wall. While I-SCC is extremely rare in underground petroleum pipelines all other plausible cracking mechanisms had been eliminated through a detailed metallurgical analysis. The agent responsible for the I-SCC was suspected to be methanol? which is believed to have been used as a drying agent during the commissioning pneumatic test on the pipeline. Following the completion of the metallurgical investigation a laboratory research program was initiated to confirm the mechanism of methanol cracking and to simulate the environmental conditions necessary for methanol-induced I-SCC to occur. Furthermore another investigation was launched on two sections obtained from the Line in 2013 to quantify the distribution of residual stresses a potential contributing factor to the cracking mechanism. This paper provides an overview of the detailed metallurgical analysis and the subsequent research programs.