Provided are a pressure medium oil, containing a Group-14 element-containing organic compound selected from an organic germanium compound, an organic tin compound, and an organic lead compound, and a method for using a pressure medium oil, which includes applying a pressure to a substance via the pressure medium oil. The pressure medium oil does not solidify even under an ultrahigh pressure of more than 3.7 GPa at room temperature (25° C.) and has a low pour point, and hardly dissolves a conductive paste.

Disclosed is a lubricating engine oil composition comprising a lubricating oil base stock as a major component, and at least one metal or metalloid hydrogen atom donor compound. Also disclosed is a method for preventing or reducing low speed pre-ignition in a direct injected, boosted, spark ignited internal combustion engine, and the use of at least one metal or metalloid hydrogen atom donor compound in a lubricating engine oil composition for preventing or reducing low speed pre-ignition in a direct injected, boosted, spark ignited internal combustion engine.

Provided are a pressure medium oil, containing a Group-14 element-containing organic compound selected from an organic germanium compound, an organic tin compound, and an organic lead compound, and a method for using a pressure medium oil, which includes applying a pressure to a substance via the pressure medium oil. The pressure medium oil does not solidify even under an ultrahigh pressure of more than 3.7 GPa at room temperature (25 C.) and has a low pour point, and hardly dissolves a conductive paste.