Systems and methods for determining a concentration of biodiesel in a mixture of biodiesel and petrodiesel are provided. In one exemplary embodiment, a method includes receiving an oscillatory signal at an inductance-capacitance-resistance circuit. The circuit has a sensing element fluidly communicating with the mixture of biodiesel and petrodiesel. The method further includes generating a resonant current at a resonant frequency utilizing the circuit in response to the oscillatory signal. The method further includes determining a concentration value indicating the concentration of the biodiesel in the mixture based on an amplitude of the resonant current and/or the resonant frequency, utilizing a microprocessor. The method further includes storing the concentration value in a memory device, utilizing the microprocessor.