Mass ratios of BBH mergers from SMT evolution are confined to the range from ∼0.3 to ∼3, determined by the physics of stable binary interactions. We plot the BBH mass ratios q_{BH − BH} as a function of the BBH mass from our binary MESA grids, where q_{BH − BH} is defined as M_BH; 1/M_BH; 2 and with M_BH; 1 (M_BH; 2) as the mass of the first (second) born BH. Hatched regions indicate the combinations of BBH masses and mass ratios that cannot be produced via SMT evolution (see text). This results in a positive trend between q_{BH − BH} and M_tot. Circles indicate models in which the SMT interaction was initiated by a MS donor (case A) and diamonds mark SMT evolution from a post-MS donor (case B or C). The color indicates the orbital period at the BH+O-star stage (i.e., before the SMT). Based on binary grids of BH+O-star systems with M_BH; 1 = 4, 7, 10, 13, 16, 20, 24, 28, 32, 36 M_⊙, and 40 M_⊙.