Abstract: An optical fibre pressure sensor in which two or more lengths of side-hole fibre (1, 2) are joined together at their ends, in which at a joint (3) the two pieces are rotated relative to one another around their common longitudinal axis, in which one or more lengths of side-hole fibre have their holes (5) sealed, and in which one or more lengths of side-hole fibre have their holes (4) exposed to the same pressure as is external to that length of fibre.