Abstract: The causes of collapse of oil tanks are analyzed, and the analyitical results show that the excessive subatmospheric pressure is the main cause for collapse of oil tanks. The various factors inducing excessive subatmospheric pressure cited in the paper are as follows; for the mechanical breather valve-unqualified installation accuracy, improper routine maintenance, increamental resistance of motion induced by air/oil vapour corrosion; for the other causes-unmatchable breathing volume and inlet/outlet oil volume after tank modification, and the extreme rise of subatmospheiuc pressure caused by insufficient filling air due to sudden change of weather and air contract. These factors resulting from impeded breathing and blocking of breathing system are the direct causes for the collapse of oil tanks. Four collapse cases induced by a sudden change of temperature are given, and the peculiar factors of collapse for underground storage caven introduced. It is considered that the collapse accidents are basically induced by maloperation, and that the acci-. dents will be avoid provided the standards and regulations concerned be carried out strictly.