Solid-solid phase transitions in petroleum waxes with different melting points have been studied using Fourier Transform Infrared (FT-IR) spectroscopy and calorimetry. The temperatures and enthalpies of these transitions have been measured and their manifestation in the temperature dependent IR spectra have been identified. It is found that the number of phase transitions as well as their enthalpies depend on the n-paraffins distribution in the wax. These solid-solid phase transitions have been shown to govern the temperature dependence of hardness, as measured by needle penetration, of the wax. The phase transitional parameters have been correlated with the average chain length and the variation of transition temperature with a composition related parameter, a, obtained from the carbon number distribution in the wax, has been studied.