A fiber optic sensor for sensing the presence of an analyte has a plurality of optical fibers each of which has an analyte sensing segment and the fibers are deployed so that the analyte sensing segments are arranged in sequential offset relationship over a distance such that each segment is available for detecting the analyte over a part of the distance. This has the advantage that detection of an analyte can be spatially resolved to the location of the one or more segments that have responded to the presence of the analyte. It also has the advantage that the high attenuation of sensing segments is reduced due to the smaller distance traversed by each sensing segment. Also multiple sets of such fibers may be deployed in order to detect multiple analytes, each set being constructed for a particular analyte. Also a fiber carrying structure is shown that allows the sensing segments to be available for detection of analytes and to conduct lead portions of the fibers to and from the sensing segments. A system also employs light energy sources and detectors and a processor for determining response of a sensing segment to an analyte exposure.