Petroleum oil pesticides are used as acaricides, insecticides, and herbicides. Oils can cause phytotoxicity if oils contain unsaturated hydrocarbons. Traditional chemical methods to determine unsulfonated residue (UR), such as the ASTM D483 and MT (57), depending on sulfuric acid 98% reagent. The present study introduces a new optical spectroscopic method using FTIR to determine unsaturated Petroleum oil pesticides. The integral intensities of the bands at about 1640 to 1643 cm−1 correspond to ν(C=C). In alkynes, (C≡C 2140-2100 cm-1). Three technical petroleum oil samples are collected from three different companies in Egypt. (El-Mostakble for Chemicals Co.(S1), Kafr El-Zayate for Pesticides and Chemicals (KZ)(S2), and Misr Petroleum Refining Co(S3). FTIR results showed peaks demonstrated more absorbance while transmittance decreased in all samples at 1643 to 1640 cm-1 and 2121 cm-1 when adding 1-octene 99% and 1-Heptyne 99% to the oil of all samples. Therefore, FTIR can detect and determine unsaturated technical petroleum oils. Moreover, the method of FTIR has advantages in preventing exposure to the toxicity of acids and can differentiate between carbon double bond and triple bond