Abstract: A bundle of fiber-optic sensors that resist breakage, for use in measuring pH, CO.sub.2, and O.sub.2 concentration, and a method of making the same. Three otpical fibers are enclosed in a common polyimide sheath and extend parallel to one another toward a distal end of the sensor, where they are bonded together in a mutually supportive array. At the distal end of one of these optical fibers is disposed a pellet comprising a CO.sub.2 analyte indicator molecule codissolved within a polymer matrix. A thin reflective surface of gold foil is provided on the pellet such that incident light transmitted through the optical fiber and polymer matrix is reflected back into the optical fiber. The CO.sub.2 polymer matrix absorbs light of a given wavelength to an extent dependent upon the level of CO.sub.2 present.