Various energy sources are positioned as sustainable, assuming this may elicit positive evaluations of these sources, particularly among people who care about nature and the environment (i.e. have strong biospheric values). For example, the gas industry and some politicians position gas as a relatively clean fossil fuel and as a transition fuel towards future sustainable energy systems. But will people, particularly those who strongly endorse biospheric values, positively evaluate every energy development that is promoted as sustainable? We studied how sustainability claims affect evaluations of gas in the Netherlands. In line with what is commonly stated in practice, in a scenario study, we either presented natural gas as a relatively clean fossil fuel in current energy systems, or as a transition fuel in future energy systems with an increased share of renewables. Interestingly, stronger biospheric values were not associated with more positive evaluations of natural gas in either of these conditions. Yet, the stronger their biospheric values, the more positively respondents evaluated gas innovations, namely green gas and power-to-gas, which do not rely on fossil fuels. The findings demonstrate that merely sustainability claims may not allay the concerns that people have about the environmental consequences of some energy developments.