The preparation of P&ID as-built, PFD, “cause and effect” diagrams of Opet Marmara terminal, the largest fuel storage facility in Turkey, was realized by Gizil Enerji team. In this project, one of the important examples of reverse engineering, smart piping and instrument diagrams (P&ID) were created using AutoCAD Plant software by Gizil Enerji site survey and CAD teams. This project is strategically important in terms of learning best practices in tank farms.