More and more sour reservoirs are being developed. As these reservoirs are often deep, there is an increasing need for higher strength, sour service drill strings. This paper addresses the philosophy of new recommended practices in Canada for critical sour service drilling, giving materials performance requiremems. Included are requirements for a new, sour service 724 MPa (105 ksi) grade drill pipe. Keywords: sulfide stress cracking, drill pipe, coiled tubing, drill stem components, underbalanced drilling, hydrogen sulfide, TM0177, steel.