Under the conditions where the predicted ZT max are obtained, Bi 2 SO 2 and Bi 2 SeO 2 have very similar Seebeck coefficients, and the similar ZT max are a balance of a lower conductivity but also a lower thermal conductivity in the selenide. Bi 2 TeO 2 is predicted to have a similar S to the sulphide and selenide but a much larger σ which, despite its larger κ el , results in an overall higher ZT max . cm -3 on the same order as typical doping levels achieved in experiments on n-type Bi Interestingly, the larger S obtained with p-type doping results in much higher predicted ZT max for Bi 2 SO 2 and Bi 2 SeO 2 . At a comparable n = 5 × 10 19 cm -3 to the doping levels achieved with n-type doping in experiments, we predict ZT max = 0.72 and 1.12 should be achievable for the sulphide and selenide, respectively, which are 2 -2.5× larger than the ZT max predicted for n-type doping. With even larger n > 10 20 cm -3 to compensate for the lower σ obtained with p-type doping we predict ZT max = 2.53 and 2.62. A benchmark ZT > 1 requires requires heavy doping, with n on the order of 10 20 cm -3 or above, for both Bi 2 SO 2 and Bi 2 SeO 2 , but, depending on n, can be achieved at moderate T > 500 K. While larger than typical n-type doping levels, the heavy p-type doping n are comparable to those achieved in experiments on p-type LaCuOSe and BiCuOSe. For Bi 2 TeO 2 , we predict higher p-type ZT max = 1.36 and 1.51 can be achieved with n = 5 × 10 19 and 10 20 cm -3 , and that ZT > 1 can be obtained with a more modest range of doping levels and a slightly wider temperature range of T > 400 K compared to Bi 2 SO 2 and Bi 2 SeO 2 . As for the sulphide and selenide, part of the larger ZT max is due to a larger S, but the higher doping level also leads to a σ comparable to the n-doped material but with a much lower κ el .