Fuel adulteration, the practice of blending lower-quality substances like kerosene with gasoline, poses significant challenges for ensuring fuel quality and safety. This study investigates two electromagnetic-based methods for detecting such adulteration: the open-ended coaxial line method and the circular waveguide method. The results reveal that the open-ended coaxial line technique is particularly effective in detecting kerosene contamination, identifying levels as low as 10% by measuring changes in the dielectric constant of the gasoline-kerosene mixture. Operating in the frequency range of 0.25–1.25 GHz, this method captures subtle changes in permittivity. In contrast, the circular waveguide method evaluates contamination by monitoring shifts in the resonance frequency of the mixture within the 10.5–11.25 GHz band, effectively identifying higher levels of contamination exceeding 10%. The resonance frequency data from this method were analyzed using linear polynomial regression, achieving a high level of accuracy with a coefficient of determination (R²) of 0.9883. These findings highlight the effectiveness of both methods in detecting fuel adulteration, with the open-ended coaxial line method showing higher accuracy in detecting lower contamination levels.