How are basic personality traits linked with individual differences in competitiveness? We examined extraversion and agreeableness, as well as their lower-level aspects (i.e., assertiveness, enthusiasm; compassion, politeness), in relation to both self-reported competitiveness and competitive bidding within two auction games. Participants (N = 304, 56% female) completed comprehensive assessments of personality and competitiveness, along with two hypothetical auction games (a standard “Winner-Pay” auction, and a riskier “All-Pay” auction). Extraversion positively predicted self-reported competitiveness whereas agreeableness was a negative predictor, and also predicted less competitive auction bidding. At the aspect-level, assertiveness (but not enthusiasm) positively predicted self-reported competitiveness as well as escalation in bidding within both auctions. Compassion (but not politeness) predicted less competitive auction bidding whereas politeness (but not compassion) predicted lower self-reported competitiveness. Future research is needed to determine whether these findings generalise beyond the lab to competitive behaviour as it occurs in the wild.