Main marine & utility (M & U) systems are essential to the routine operation of offshore units,and are extremely important as they are the system that will ensure the basic safety of offshore platforms. This paper gave a general explanation and guideline of the marine & utility systems in offshore projects including their interface with topside,M & U engineering,equipment sizing operation and control. Main marine & utility (M & U) systems are essential to the routine operation of offshore units, and are extremely important as they are the system that will ensure the basic safety of offshore platforms. This paper gave a general explanation and guideline of the marine & utility systems in offshore projects including their interface with topside, M & U engineering, equipment sizing operation and control.