There is growing recognition of the need to understand public attitudes to energy sources, such as shale gas, and to feed these into decision-making. This study represents the first detailed UK experimental survey of public perceptions of shale gas fracking, including analysis of the effects of different messages and the relative influence of different audience, message and contextual factors on support and risk perceptions in respect of shale gas fracking. Using an online survey (N = 1457) of the UK public, we find considerable ambivalence about shale gas, but also greater awareness of potential risks than benefits. Prior knowledge is associated with more favourable attitudes, although demographics, political affiliation and environmental values are strongest influences on perceptions. When provided with environmental or economic information about shale gas, participants became more positive - irrespective of their prior values or whether information is framed in terms of losses or gains. As expected, prior attitudes predict how information is received, with more attitude change amongst the most ambivalent respondents. We conclude that additional information about shale gas is more likely to be effective changing attitudes if focussed on this 'undecided' group. Studies of this type are important for policy makers and industry alike.