A study has been undertaken to understand the effects of blending high-viscosity fresh and used corn oils with diesel and jet fuel mixed with butanol and ethanol on combustion emissions such as NOX and CO. Several corn oil-based blends were formulated, characterized, and compared to understand the effect of composition on viscosity, fuel stability and energy content. The formulated corn oil blends were combusted in a 30 kW modified combustion chamber to determine the corresponding NOx and CO emission levels. Used corn oil was made and characterized by quantifying its total polar material (TPM), iodine value, free fatty acid content, and peroxide value. The combustion experiments were conducted at a constant heat output of 19 kW to observe and study the effects of equivalence ratio, swirl number, and fuel composition on emissions. Used corn oil blends exhibited better combustion performance than fresh corn oil blends, due in part to the higher unsaturation levels in fresh corn oil. NOx emissions for used corn oil increased with swirl number. The combustion experiments also revealed that higher amount of diesel (lower amount of corn oil) results in higher NOx emissions. All corn oil-based blends showed a generally decreasing carbon monoxide (CO) trend at both swirl numbers at very lean conditions. The results also indicate that used corn oil can be combusted efficiently when mixed with diesel or jet fuel resulting in low NOx levels.