We present an optical fiber chemical sensor based on gold- island surface plasmon excitation. The sensing part of the fiber is a one inch portion on which cladding has been removed and onto which a thin layer of gold (40 angstroms) has been deposited to form a particulate surface. Annealing the gold reshapes the particles and produces an absorbance near 535 nm when the only medium residing outside the surface is air. A range of wavelengths provided by a white light source and monochromator is launched through the optical fiber. The transmitted spectra display shifts in the resonance absorption due to any changes in the medium surrounding, or adsorbed onto the fiber. Experimental results for the sensitivity and dynamic range in the measurement of liquid solutions are in agreement with a basic theoretical model which characterizes the surface plasmon using nonretarded electrodynamics. Furthermore, the model assumes the particles are isolated oblate spheroids with a distribution of eccentricities.