In the winter 1999 - 2000, Chevron Canada Resources, Calgary, successfully completed a hot tap on the Simonette high-pressure sour gas transmission line near Grande Prairie, Alta. The hot tap was required to bring new production into the Simonette pipeline without shutting in existing production. It was completed under full line pressure and gas-condensate flow with temperatures averaging -20 deg C. The job demonstrated that such hot tapping on spour gas lines can be completed safely under proper procedures. In this hot tap, Chevron Canada had a technical advantage by having a section of the original pipe, all the line material test reports, and HIC (hydrogen-induced cracking) resistant steel. Design pressure of the 12-inch, Grade 359 Cat II Simonette pipeline is 9,930 kPa and the line operates at 8200 kPa. The gas in the main transmission line is approximately 2 % H2S and 4 % CO2. The gas being brought on through the 4-inch hot tap tie-in was 21 % H2S and 5 % CO2. At the tie-in point the transmission line temperature was 3 deg C. Safely welding on the pipeline under these conditions posed a considerable technical challenge. In welding of sour service lines, it is critical that the final weld hardness be less than Vickers 248 microhardness. This can be very difficult to achieve during welding on a line transporting a quenching medium of gas and condensate. In addition, hydrogen charging of the steel from operation in sour service can lead to hydrogen embrittlement during welding. Ludwig and Associates, Calgary, developed the hot-tap procedure and extensively tested it to ensure that suitable weld micohardness was achievable under pipeline operating conditions.