Wild oat (Avena fatua) is a grass weed species that infests cropland. Common post-emergent herbicides for controlling wild oat are those that inhibit acetyl-CoA carboxylase (ACCase) and acetolactate synthase (ALS). Variation among plastidic ACCase gene sequences of herbicide-susceptible wild oat biotypes USDA96 and KYN119 revealed ACCase gene diversity consistent with possible separate diploid ancestry, with KYN119 more likely to share diploid ancestry with herbicide-resistant UM1. USDA96 wild oat shows low-level tolerance to the ALS-inhibiting herbicide flucarbazone, and the inheritance of this tolerance was studied among F3 families generated from KYN119 and USDA96 reciprocal crosses. Quantitative inheritance was observed at the below-label flucarbazone rate of 1.81 g ai/ha. Some F3 families had higher post-treatment main shoot dry weights than either parent, which may be due to heterosis and/or genetic contributions from both parents. No evidence for association between the Acc1;1 ACCase gene and low-level tolerance to flucarbazone was observed.