This study examines the mechanical safety of a gas lift completion string in a certain oil eld, Algeria 438B block, having complex geological characteristics (a high salt and high-pressure sandwich). When an annulus is not supported within uid column after unloading by using conventional single-tube gas lift completion with positive lift oil production, inner pressure is so low that the pressure di erential between the annulus and external casing is very large, which may damage the casing. Hence, a dual tube completion annulus lled with uid that can resist pressure was used to overcome this problem in adjacent blocks using a gas lift production string with positive and reverse lift oil. However, this technology is complex and characterized by poor system reliability, large construction costs, and maintenance diculty. By considering the three aspects of a casing string, squeeze strength, tensile strength, and internal pressure strength, a gas lift completion string with dual concentric tubes and positive lift was preferably selected under conditions that were veri ed to be safe for production and a shut-in state. This gas lift completion string design was shown to be feasible and had no problem of completion string in adjacent blocks.