This thesis has studied the low-temperature atmospheric pressure plasma as a potential technological application for the degradation of waste oils. The study has been approached initially by investigating the degradation of oil in gas phase only, in order to understand the gas chemistry and elucidate the plasma-chemical degradation mechanism. Gaseous odourless kerosene and dodecane have been used as simulants to waste oil and their plasma-chemical degradation has been studied using a BaTiO3 packed bed plasma reactor and a gliding arc discharge reactor. Kerosene showed similar degradation behaviour to dodecane and the latter one was chosen as a surrogate to allow quantitative analysis. The dodecane plasma degradation efficiency and the distribution of end-gaseous products have been studied under these two reactors in different gas compositions. Optical emission spectroscopy was used to identify intermediate excited species and calculate the rotational and vibrational temperature profiles. Differences in the dodecane degradation gas chemistry between the packed bed and the gliding arc plasma are discussed and postulated mechanisms are presented for each condition. Gliding arc discharge demonstrates higher degradation efficiency and it will be used mainly for the plasma-liquid treatment. The plasma-liquid dodecane treatment is firstly studied using argon dielectric barrier discharge. The effect of different reactor configuration, humidity and temperature to the discharge characteristics and degradation efficiency will be discussed. The study of the liquid dodecane degradation is extended by using the gliding arc discharge. Using N2 and Ar in both dry and humid conditions for the batch treatment of dodecane, the degradation efficiency, gas chemistry and liquid chemistry are discussed and correlated to the gas chemistry observed during the plasma treatment of gaseous dodecane under the same conditions, in order to gain an overall understanding of the plasma-liquid clean-up process.Finally, the gliding arc plasma treatment of liquid dodecane is studied using the recycling method and shows a significant improvement to the degradation efficiency.