Methane is commonly found in sedimentary basin at temperatures of at least 473 K. Accurate values of diffusion coefficients for methane in water at high pressure and elevated temperature are essential to our understanding of transport behavior of methane in pore spaces at reservoir conditions. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusion coefficients of methane in water were determined under high pressures (up to 40 MPa) and wide temperature range (from 273 to 473 K) via Raman spectroscopic method. The relationship between diffusion coefficient of methane in water [D(CH4) in m(2)/s] and temperature (Tin K) was derived with Speedy-Angell power-law approach as: D(CH4) = D-0 [T/Ts - 1](m) where D-0 = 15.95 x 10(-9) m(2)/s, Ts = 229.8 K, m = 1.8769. At constant temperature, pressure has very small effect on the diffusion coefficients. (C) 2013 Elsevier B.V. All rights reserved.