The rapid expansion of coal seam gas (CSG) extraction across Australia has polarized public opinion about the risks, benefits, and the future of the industry. We conducted a randomized controlled experiment to assess the impact of CSG messaging on opposition to the CSG industry. Residents of a major Australian city (N = 549), aged between 21 and 87 years, were randomly assigned to view one of three brief video messages (pro-CSG, anti-CSG, or a neutral control) sourced from the Internet. They then completed measures assessing CSG affective associations, perceived risks and benefits of CSG, and degree of opposition to the CSG industry. A subsample of 317 participants also completed the measures of affect, risks, benefits, and opposition two weeks following the initial message presentation. Message type significantly predicted message effects in a pattern consistent with the affect heuristic model, although overall, the message effects were modest in magnitude. Respondents who viewed the anti-CSG video (relative to the control) reported more negative affective responses to CSG, perceived higher risks, fewer benefits, and greater opposition to the CSG industry. Those who viewed the pro-CSG video (relative to the control) reported stronger positive affective responses to CSG, perceived more CSG benefits and fewer risks, and expressed less opposition to the industry. The effects persisted over a two-week interval for the anti-CSG message, but not for the pro-CSG message. Our findings suggest that people's risk perceptions and views about the acceptability of CSG are malleable by messaging that targets affective pathways.