Corrosion is a great problem in petroleum industry for both upstream and downstream; whereas, it damaged the petroleum equipment such as storage tanks, separator units, pipelines, pumps etc.. This paper is highlighted and pay attention to preserve and protect them from damage caused by corrosion throughout a case study in the storage tanks of Tobruk refinery. Cathodic protection is an effective corrosion protection technique that uses the electrochemical properties for equipment protection. The protection is achieved via the cathode of the electrolytic cell whereby the other end is the anode of the cell. This study was conducted for protecting (365,000bbl) crude oil storage tank exists in Tobruk terminal. The scope of work included the design and determination of all necessary materials for the internal and external cathodic protection of tank bottom utilizing aluminum anodes as sacrificial anodes. It has been revealed through the results of the design this method was designed to suitable requirements of the crude oil industry which was rapidly development in the recent period. The calculation results revealed that the cathodic protection required (71) anode rods (N), the current output of one anode is 0.333 amp, the current output is 23.64 amp, protect area for one anode about 52.595 m2, minimum distance between anodes (L) m 7.25 m and protecting diameter for one anode (D) anode is 4.09 m.