Water scrubbing is the most widely used technology for removing CO2 from biogas and landfill gas. This work developed a rate-based mass transfer model of the CO2-water system for upgrading biogas in a packed bed absorption column. The simulated results showed good agreement with both a pilot-scale plant operating at 10 bar, and a large-scale biogas upgrading plant operating at atmospheric pressure. The calculated energy requirement for the absorption column to upgrade biogas to 98% CH4 (0.23 kWh Nm(-3), or 4.2% of the input biogas) is a significantly closer approximation to the measured value (0.26 kWh Nm(-3), or 4.8% of the input biogas) than has previously been reported in the literature. The model allows for improved design of CO2 capture and biogas upgrading operations and can also be a useful tool for more detailed cost-benefit analysis of the technology.