<p>Underground coalbed methane (CBM) extraction is critical for mitigating gas-related hazards and enhancing clean energy recovery from coal seams. The effective extraction radius is a fundamental parameter for designing an efficient borehole layout; yet, its determination is significantly complicated by competitive interference among adjacent boreholes, a phenomenon that remains inadequately quantified. In this study, a mathematical model for gas transport is developed that incorporates the Klinkenberg effect. To quantitatively assess the impact of inter-borehole competitive interference on the effective extraction radius, the radius deviation coefficient (RDC) is proposed. The influences of the initial permeability and initial gas pressure on the RDC are systematically analyzed. The results show that, as the initial permeability increases, the effective extraction radius increases for both single-borehole and multi-borehole extraction conditions, whereas the RDC decreases, suggesting that competitive interference between boreholes becomes more pronounced in high-permeability coal seams. In contrast, as the initial gas pressure increases, the effective extraction radius decreases significantly in both borehole configurations, and the RDC clearly has an inverse relationship with the initial gas pressure. Finally, the mechanism of competitive interference among boreholes during gas extraction is elucidated, and the methodology for determining the effective extraction radius in underground CBM extraction is discussed. This study provides a quantitative basis for optimizing borehole layouts to enhance underground CBM extraction and mitigate gas-related risks in underground coal mines.</p>