<div>Determination of the chemical composition of liquid transportation fuels emerged as a novel and important field of study after the introduction of advanced analytical instruments, which are capable of very detailed chemical analyses of complex mixtures. Aviation fuels make up a crucial portion of liquid transportation fuels. There are several significant challenges in the field of aviation fuels, including the development of optimal analytical methods for the determination of the chemical compositions of the fuels, fuel properties measurements, and correlations between fuel properties and chemical composition. This dissertation explores possible correlations between fuel chemical composition and its properties and proposes novel approaches. First, a detailed description of a method for the determination of the detailed chemical composition of all middle distillate fuels (diesel and aviation fuels) is presented. Second, the density was correlated to fuel composition. Additionally, the approach of measuring the density, the hydrogen content, and the carbon content via a GC×GC-FID was introduced. Lastly, it was discovered that minute differences in chemical composition can influence fuel properties. This finding is described in the last chapter, where three HEFA samples were investigated. </div>