Curiosity in the properties of non-Gaussian beam-based optical devices has seen a recent resurgence on account of large volume of higher order modes as supported by the platform. By harnessing the advantages of higher-order Bessel-Gauss beam, the present research unveils the concept of an extremely-sensitive optical sensor to detect the limit of kerosene adulteration in petrol. The sensory method works on the concept of modal interference, in which the transmitted power differs with changeable cladding refractive index as induced by the varying kerosene concentration in petrol. To corroborate this, the commercially available Lumerical’s Mode solution software and its Eigenmode expansion solver were exploited to investigate the transmitting property of the sensing device. If the sensing length is set to 7 cm, the procured average sensitivity of 0.41 dB/% is 4.1-fold higher in contrast to the typical Gaussian beam-shined sensor. The presence of ~0.02% kerosene contaminant in petrol can be sensed with the proposed methodology, while the conventional Gaussian beam-shined technology is able to sense the presence of ~0.10% of the same. Therefore such a nascent-class of beam called higher-order Bessel-Gauss beam accelerates new possibilities in the area of fiber optic sensing and can be useful in various petrochemical and automotive industries.