The transport sector is a major contributor to the global greenhouse gas and pollutant emissions, owing to the high reliance on fossil-based fuels. In light of this, the search for sustainable alternative fuels is imperative. Oxygenated fuels have been proposed as a potential solution for their sustainable nature and clean combustion properties. However, it is crucial to understand the potential pollutants (particularly soot) generated during the combustion of oxygenated fuel because of their distinct chemical composition when compared to fossil-based fuels. To have a through investigation on oxygenated fuel combustion and its impact on soot formation, three different combustion systems are examined to determine how oxygenated fuels affect soot formation in this thesis. Experimental methods including colour-ratio pyrometry, differential mobility spectrometry, Raman spectroscopy, and thermogravimetric analysis are used to characterise the effect of oxygenated fuels on soot formation. The first study focuses on the impact of blending proportions of oxygenated fuels on soot formation under laminar coflow diffusion flames. Polyoxymethylene dimethyl ethers (PODE_n) were chosen to be studied because they are one of the emerging class of oxygenated fuels for the transport industry. Up to 20% of PODE₃ was blended to ethylene to generate the flames to perform flame temperature, soot volume fraction, and particle size distribution measurements. The 5% PODE₃ blend showed a synergistic effect in the formation of soot, while higher blends reduced the soot volume fraction and average particle size. The formation of the initial benzene (and subsequently soot) was linked to the pathways by which the fuels decompose. In order to compare the differences between oxygenated fuels, three C3 oxygenated fuels - PODE₁, iso-propanol, and dimethyl carbonate (DMC) were studied using the same methodology as PODE₃ due to the intriguing synergistic effect observed for PODE₃. The C3 oxygenated fuels exhibited distinctly different degree of the synergistic effect on soot formation at the same blending ratio. The findings reinforce the importance in considering the fuel molecular structure in influencing fuel decomposition pathways, which in turn affect soot formation. Four oxygenated fuels - ethanol (EtOH), DMC, PODE₁ and PODE₃ - were mixed with jet fuel and investigated using wick-fed laminar diffusion flames to better understand the sooting behaviour of oxygenated fuel mixtures in a more complex chemical environment. Regardless of the type of oxygenated fuels, it was discovered that the sooting tendency (as measured in accordance with ASTM D1322) generally correlated with the soot volume fraction and particle size distribution measurements. The ability to relate data gathered using the ASTM D1322 standard for the sooting behaviour of different mixtures will be beneficial for the aviation industry upon the switch to sustainable fuels. Finally, under a compression ignition engine, the morphology and nanostructure of soot generated from the combustion of oxygenated fuels (EtOH, DMC, PODE₁ and PODE₄) with jet fuel were investigated. It was revealed that the dilution effect, combustion condition effect, and chemical effect are all possibilities in which the blending of oxygenated fuels affects the properties of soot. Particularly, the type of oxygenated species produced during the combustion of oxygenated fuels can have a significant impact on the soot properties.