Petroleum, which is one of the most complex mixtures existing in nature, is equilibrated and coexists with the aqueous phase at reservoir conditions. However, depending on the oil viscosity, strong emulsions may be formed due to the high shear imposed by the production process. As a consequence higher temperatures conditions are necessary for the oil separation treatment. Therefore it is important to assure that scale inhibitors are thermally stable and able to act in what are considered extreme temperatures such as the ones used in heat exchangers, for example 16 °C. This work aimed to evaluate the influence of temperature in the scale inhibition activity for different active materials of chemical inhibitors, such as: Nitrilotris (methylene) tri phosphonic acid (NTP), Diethylenetriamine penta (methylphosphonic acid) (DETPMP), and polyvinyl sulphonate (PVS). Aqueous inhibitor solutions were aged in the temperature conditions between 60 to 160 °C for different times (6, 12 and 24 hours). Raman spectroscopy, NMR (31P, 1H and 13C) and FT-MS techniques were used to characterize chemical species from aged and original inhibitor solutions. Different from previous works, these techniques allow identification of some degradations products. Additionally, dynamic performance tests were conducted to evaluate scale inhibitor performance of the solutions. Results of the chemical characterization of the original and thermally aged PVS showed no compositional differences. Dynamic testing for barium sulphate scale showed that minimum effective concentrations remained constant in all assays. However, for the NTP and DETPMP products, at the highest temperature (160 °C, after 24 hours of testing) some degradation products were identified, such as methyl phosphonic acid, and especially, amino methyl phosphonic acid. As a consequence of the structural breakdown of the phosphonate molecules, confirmed by chemical analysis using FT-MS and NMR, the efficiency of inhibition of barium sulphate scale was reduced. The paper presents a methodology to evaluate and understand the behavior of different chemical inhibitors for extreme temperature conditions and highlights the demand for new stable molecules for high temperatures.