esters derived from oleyl alcohol particularly preferable examples of oleic acid ester include isopentacosyl oleate and 1 6 hexanediol dioleate and particularly preferable examples of oleyl alcohol ester include dioleyl adipate when aliphatic acid ester is used together this invention does not impose any limitation as to its mixing rate but it is preferable if their weight ratio is inside the range of aliphatic acid ester organic phosphoric acid ester compound 50 50 95 5 when a lubricant according to this invention is applied to synthetic fibers it is heated to 40 80 u00b0 c to make it into a uniform liquid and applied in the neat condition at a rate of 0 1 3 0 weight with respect to the synthetic fibers for causing the lubricant according to this invention to adhere to synthetic fibers known prior art lubricating methods may be used such as the roller oiling method the guide oiling method and the spray oiling method examples of synthetic fibers to which the lubricants and the processing methods according to this invention can be applied include polyamide filaments polyester filaments polyacrylonitrile filaments and polyolefin filaments but it is preferred to apply them to polyamide or polyester filaments it is particularly preferable to make the application between the spinning process and the drawing process the methods according to this invention are particularly effective when applied to synthetic fibers which undergo a spinning process under a condition of high temperature and high.