Recently, the possibility of realizing a subsurface bio-reactor has been realized since microbial methanogenesis has been confirmed in diverse subsurface environments such as coalbeds or petroleum reservoirs. We propose a new gasification method for use in subsurface environments, known as the Subsurface Cultivation and Gasification (SCG). SCG was devised based on the production of biogenic methane gas in subsurface environments. This approach employed hydrogen peroxide to decompose organic matter rapidly. Conversion of organic matter from source rocks into biomethane with the help of microorganisms is expected to be highly profitable. In this study, a series of batch tests using a hydrogen peroxide (H₂O₂) solution were performed on lignite to estimate the potential of low-molecular-weight organic acid production. The effects of several factors on the production of low-molecular-weight organic acids have been considered, such as, concentration of H₂O₂, temperature, liquid-solid ratio, and specific subsurface area of lignite. It was found that the quantity of low-molecular-weight organic acids depended on temperature, liquid-solid ratio, and specific subsurface area of lignite; however, there isn't a unique relationship between them and the H₂O₂ concentration. Moreover, the mass of lignite reduced remarkably when batch tests were performed with a high concentration of H₂O₂. If H₂O₂ is to be injected into a target seam with the SCG method, we should estimate the optimum H₂O₂ concentration to produce low-molecular-weight organic acids with taking into consideration the mechanical stability of the target seam as well as the subsurface environmental chemical reaction with a geological improvement.