An optical sensing system for sensing hydrogen in a fluid, adapted for employing measurement values of at least two differing optical sensors (11a, 11b), comprising: - a first optical sensor comprising a first optical fiber, wherein an end portion of the first optical fiber is coated with a first multilayer on an end surface perpendicular to a longitudinal axis of the first optical fiber, the first multilayer being adapted to change its optical reflectance, dependent on a hydrogen partial pressure in the fluid and dependent on a temperature of the fluid, with a known first characteristic being a first parameter matrix of isobars of hydrogen partial pressure, temperature and optical reflectance; - a second optical sensor comprising a second optical fiber, wherein an end portion of the second optical fiber is coated with a second multilayer on an end surface perpendicular to the longitudinal axis of the second optical fiber, the second multilayer being adapted to change its optical reflectance, dependent on the hydrogen partial pressure in the fluid and dependent on a temperature of the fluid, with a known second characteristic being a second parameter matrix of isobars of hydrogen partial pressure, temperature and optical reflectance, which is different from the first characteristic; - at least one light source adapted for coupling light into the first optical fiber and the second optical fiber, - at least one light detector adapted for detecting a light intensity reflected by the first multilayer and a light intensity reflected by the second multilayer, - a control unit operably coupled to the at least one light detector, adapted for calculating the hydrogen partial pressure in the fluid by using the detected light intensity reflected from the first multilayer and the detected light intensity reflected from the second multilayer to determine, from the first parameter matrix and the second parameter matrix, for which hydrogen partial pressure and temperature there is a fit in both the first parameter matrix and the second parameter matrix. - a first optical sensor comprising a first optical fiber, wherein an end portion of the first optical fiber is coated with a first multilayer on an end surface perpendicular to a longitudinal axis of the first optical fiber, the first multilayer being adapted to change its optical reflectance, dependent on a hydrogen partial pressure in the fluid and dependent on a temperature of the fluid, with a known first characteristic being a first parameter matrix of isobars of hydrogen partial pressure, temperature and optical reflectance; - a second optical sensor comprising a second optical fiber, wherein an end portion of the second optical fiber is coated with a second multilayer on an end surface perpendicular to the longitudinal axis of the second optical fiber, the second multilayer being adapted to change its optical reflectance, dependent on the hydrogen partial pressure in the fluid and dependent on a temperature of the fluid, with a known second characteristic being a second parameter matrix of isobars of hydrogen partial pressure, temperature and optical reflectance, which is different from the first characteristic; - at least one light source adapted for coupling light into the first optical fiber and the second optical fiber, - at least one light detector adapted for detecting a light intensity reflected by the first multilayer and a light intensity reflected by the second multilayer, - a control unit operably coupled to the at least one light detector, adapted for calculating the hydrogen partial pressure in the fluid by using the detected light intensity reflected from the first multilayer and the detected light intensity reflected from the second multilayer to determine, from the first parameter matrix and the second parameter matrix, for which hydrogen partial pressure and temperature there is a fit in both the first parameter matrix and the second parameter matrix.