Résumé : Microbial growth in water injection systems can lead to many problems, including biofouling, water quality deterioration, injectivity loss, microbial corrosion, and reservoir formation damage. Monitoring of microbial activities is required in any mitigation strategy, enabling operators to apply and adjust countermeasures properly and in due time. In this study, the pre-industrial autonomous microbe sensor (AMS) was constructed with technical improvements from the prototype for increased sensitivity, durability, robustness, and maintainability. The pre-industrial AMS was lab validated, field proven, and deployed at critical locations of seawater injection network for automated detection of microorganisms under the Saudi Arabia’s harsh environment. An excellent correlation between AMS measurement data (fluorescence count) and actual count of microbial cell number under microscope was established (coefficient of determination, R2 > 0.99) for converting AMS fluorescence count to cell numbers (cell mL-1) in the injection seawater. The pre-industrial AMS only required monthly maintenance with solutions refill, and was able to cope with hot summer months even without protection in an air-conditioned shelter. The study team recommended wider deployment of the online AMS for real-time monitoring of bacteria numbers in the various strategic locations in Saudi Aramco’s complex seawater injection network, as an integral component of pipeline corrosion and leak mitigation program.