Objective: Near-misses are a structural characteristic of gambling products that can be engineered within modern digital games. Over a series of pre-registered experiments using an online slot machine simulation, we investigated the impact of near-miss outcomes, on subjective ratings (motivation, valence) and two behavioural measures (speed of gambling, bet size).Method: Participants were recruited using Prolific and gambled on an online 3-reel slot machine simulator that delivered a 1 in 3 rate of X-X-O near-misses. Study 1 measured trial-by-trial subjective ratings of valence and motivation (Study 1a, n = 169; Study 1b, n = 148). Study 2 measured spin initiation latencies (n = 170) as a function of the previous trial outcome. Study 3 measured bet size (n = 172) as a function of the previous trial outcome.Results: In Study 1a, near-misses increased the motivation to continue gambling relative to full-misses, supporting H1. On valence ratings, near-misses were rated significantly more positively from full-misses, in the opposite direction to H2; this effect was confirmed in a close replication (Study 1b). In Study 2, participants gambled faster following near-misses relative to full-misses, supporting H3. In Study 3, participants significantly increased their bet size following near-misses relative to full-misses, supporting H4.Conclusion: Across all dependent variables, near-miss outcomes yielded statistically significant differences from objectively-equivalent full-miss outcomes, corroborating the ‘near miss effect’ across both subjective and behavioral measures, and in the environment of online gambling. The unexpected findings on valence ratings are considered in terms of boundary conditions for the near-miss effect, and competing theoretical accounts based on frustration/regret, goal generalization, and skill acquisition.