To estimate the effect of transport process of carbon monoxide gas in liquid methanol in a two-step methanol synthesis process which starts with carbonylation of methanol to methyl formate, solution and diffusion process of CO gas and its single bubbles in liquid phase methanol were theoretically and experimentally studied under various pressures and temperatures. Diffusion coefficients of dissolved CO gas in methanol were obtained by comparing the experimental data of CO gas solution in methanol within a small glass tube with theoretical solutions based on one dimensional diffusion model. The diffusion coefficients are between 4.0×10^-9 m²/s and 7.6×10^-9 m²/s for the temperatures ranged from 30 to 80 °C, and become higher as temperature increases. In the theoretical analysis for the solution of single CO bubbles in methanol accompanying chemical absorption, the single CO bubble was assumed to be stationary and surrounded by infinite liquid methanol. The rate of solution of bubble in liquid is affected strongly by various parameters, such as solubility, diffusion coefficient, chemical reaction constant, bubble radius, especially temperature. The theoretical results show that the rate of solution of CO bubble in liquid methanol was enhanced by chemical reaction, and the total reaction rate can be improved by enhancing the transport process of gas in the liquid. They also show that the reaction constant can be obtained by comparing the experimental data of the variation of bubble radius with time with the theoretical solutions. It was understood that the theoretical nondimensional times for complete solution of the single bubbles in methanol without reaction agree well with the experimental data for the initial diameters around 0.25 mm, and the times become shorter for larger bubble diameters due to the increasing effect of nature convection induced by density difference around the bubble.