Sorption-induced changes in the localized surface-plasmon resonance (LSPR) of an n-octanethiolate-monolayer-protected gold nanoparticle film on a Si chip are exploited to differentiate two volatile organic compounds (VOC) with a single sensor. Probing the film with 488 nm and 785 nm lasers gave reflectance sensitivity ratios at the two wavelengths of 0.68 and 0.80 for toluene and n-heptane, respectively, permitting their discrimination. Swelling-induced increases in inter-particle distance appear to predominate over changes in the refractive index of the inter-particle matrix in the sensor responses. The corresponding ratios of sensitivities with a reference film of polydimethylsiloxane did not differ for the two vapors. Approaches for extending the capability for VOC discrimination by use of arrays of such LSPR sensors are discussed, along with the advantages of employing this simple platform in compact, field-deployable environmental VOC monitoring systems.