Abstract: The commercial oil bases exist non natural losses besides the natural losses. The non natural losses introduced in the paper mainly result from the management, Equipment management, regulation and rules are not well, operation doesn't follow the instruction. For the purpose of reducing losses the author presents the measures which are damper mounted in the respiration valve for new roof floating tank and for existing vault roof tank, regular inspection and check of respiration valve, recovery of oil and gas, perfect rules and regulations making etc.