Quantitative potassium species concentrations have been measured in alkali-seeded premixed methane-air flames of different stoichiometry. Potassium chloride (KCl) and hydroxide (KOH) were measured by broadband UV absorption spectroscopy and laser-induced photofragmentation fluorescence, while atomic potassium was measured using tuneable diode-laser spectroscopy. In addition, laser Rayleigh scattering was employed for temperature measurements. Investigations were made for different alkali-seeding levels and chlorine loads resulting in KCl/KOH concentrations up to similar to 30 ppm and concentrations of K atoms at ppm levels. Experimental results were compared with predictions from a chemical mechanism used in a homogenous reactor model. The observed trends, decrease in KCl and KOH concentrations and increase in K-atom concentrations with flame equivalence ratio, were well reproduced in simulations and are compared with results reported in literature. In addition, possibilities using the experimental methods for further investigations of alkali-related combustion phenomena and detailed model validation of alkali chemistry are discussed. (C) 2017 The Authors. Published by Elsevier Ltd.