Optimal Inspection/Replacement Policy for Oil and Gas Facilities:Gas Compression and Treatment System The aim of this thesis is a creation of the optimization inspection and preventive maintenance policy of oil and gas production facilities from the historical data. This thesis is a contribution to the further reliability maintenance theories for the practical application. The failure distribution type of each failure mode is defined from the real 3-year historical failure data. Including the re- distribution theory is utilized to reduce the error of nonpractical events. The probability of failure and reliability is calculated from the failure distribution.Finally, thesis generated a simple mathematic model to find the optimal inspection and preventive maintenance schedule of equipment. This model is also able to verify the reliability of the existing program and to find the inspection interval plan when the reliability of equipment is determined.