Although electronic gaming machine (EGM) jackpots are widespread, little research has yet considered the impact of this feature on gamblers' behaviour. We present the results of an in-venue shadowing study, which provided measures of player investment and persistence (e.g. number of spins, time-on-machine) from participants undertaking one or more EGM sessions on their choice of machines. 234 participants (162 female) were recruited in-venue, with half (stratified by age and gender) primed by answering questions encouraging 'big-win' oriented ideation. Primed participants were more likely to select jackpot-oriented EGMs, and primed at-risk [Problem Gambling Severity Index (PGSI) > 4] gamblers tended to select machines with a higher median jackpot prize amount than others ([Formula: see text]). Neither PGSI nor priming was associated with the rate at which participants switched machines. EGM jackpots were associated with great spend overall, and PGSI score was associated with a greater spend per play. Positive interactions were found between jackpots and PGSI, and PGSI and priming in terms of predicting greater persistence. Finally a structural model of session level variables is presented, that incorporates positive feedback between money won and number of plays in an EGM session.