The performances of two liquid level sensors based on long-period fiber gratings are studied. The long-period gratings (LPGs) have similar characteristics (length and period), but are fabricated with two photosensitive B-Ge co-doped fibers with different dopant concentrations. We investigate the temperature sensitivities of LPGs and exploit their refractive index sensitivity to implement liquid level measurement. By controlling fiber parameters, such as the dopant concentrations, the measurement sensitivity of a LPG-based fiber optic liquid level sensor can be improved.