The importance of radial losses in collisional multiple mirror confinement is investigated for arbitrary values of &bgr;. Classical radial diffusion and complete fluid stability are assumed. Analytical and numerical solutions of the coupled axial and radial diffusion problem are found. The results can be characterized in terms of a single parameter &agr;∼(&tgr;z/&tgr;x)1/2where &tgr;zand &tgr;xare average values of the axial and radial confinement times. Radial losses are unimportant for &agr;≲0.5 and improvement in overall confinement can be achieved by increasing &bgr; for these small values of &agr;. When applied to existing reactor designs, the theory shows that radial losses are significant for one‐component reactors but can be made negligible for two‐component (wetwood burner) reactors.