We report the first inert gas sensing and characterization studies based on high-resolution localized surface plasmon resonance (HR-LSPR) spectroscopy. HR-LSPR was used to detect the extremely small changes (<3 x 10(-4)) in bulk refractive index when the gas was switched between He(g) and Ar(g) or He(g) and N-2(g). We also demonstrate submonolayer sensitivity to adsorbed water from exposure of the sensor to air (40% humidity) versus dry N-2(g). These measurements significantly expand the applications space and characterization tools for plasmonic nanosensors.