Thailand is currently the world's fourth largest producer of crude palm oil. The palm oil mill effluent is proposed to be used for biogas production. A value added option is then proposed by increasing thermal efficiency of the biogas by removing CO2 content and increasing the percentage of methane, consequently turning the biogas in to green gas. In this study, the biogas and upgrading process for electricity generation with the subsidy or adder in the long term planning is presented. This analysis uses the MARKAL-based least-cost energy system as an analytical tool. The objective of this study is to investigate upgrading biogas with a selected water scrubbing technique featuring least-cost energy planning. The co-benefit aspect of biogas and biogas upgrading project is analyzed by given an adder of 0.3 Baht/kWh. The target of total electricity generation from biogas is 60 MW in 2012. The result shows that green gas will account for approximately 44.91 million m³ in 2012 and increase to 238.89 million m³ in 2030. The cumulative CO2 emission during 2012-2030 is 2,354.92 thousand tonnes of CO2. Results show that under the given adders the upgrading project is competitive with the conventional technologies in electricity generation planning. [ABSTRACT FROM AUTHOR] Copyright of Songklanakarin Journal of Science & Technology is the property of Songklanakarin Journal of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.(Copyright applies to all Abstracts.)