A pressure sensor (10) comprising fiber Bragg grating (FBG) strain sensors (12) provided within an optical fiber (14), an optical fiber strain sensor carrier rod 16 and a pressure intensifying sleeve (18). The carrier rod (16) is formed from a first glass fiber reinforced epoxy resin composite material having a first stiffness/elastic modulus the direction of strain sensing. The sleeve (18) is formed from a second composite material, having a lower axial stiffness in the direction of strain sensing than that of the carrier rod (16). Under an applied hydrostatic load, the sleeve (18) exerts an axial compressive load onto the section of rod (16) within the sleeve (18). The axial compressive strain experienced by the rod (16) is thereby increased in the region within the sleeve (18) compared to the axial compressive strain that would be produced in the rod (16) if the sleeve (18) was not present.