The present work focuses on the development and application of methodologies for (i) temperature profile characterization within a jet-stirred reactor (JSR) for quantification of uncertainty in concentration profiles measured in combustion experiments, and (ii) calculating uncertainty in species concentration used in absorption spectroscopy experiments. Temperature profiles were measured at atmospheric pressure, using a 1.6-mm-diameter K-type thermocouple positioned inside of the 30-cm3 JSR as a function of residence time, reactor temperature, and pre-heater temperature. For the spectroscopy measurements, uncertainty analysis focused on gas-phase concentrations used to determine absorption cross-sections. The JSR analysis consisted of measuring temperature profiles, T(x), for residence times of 500 ms, 1000 ms, and 2000 ms, and reactor temperatures of 500 K, 750 K, and 1200 K at 20 positions within the reactor. The measurements led to quantified thermal gradients, dT/dx, which were utilized to determine the dependence of dT/dx on volumetric flow rate and temperature.