Carbon-offset donations provide a way to mitigate the environmental damage caused by carbon emissions from aviation, but the number of fliers who choose this option is low. Information systems can support environmentally friendly decision-making in the context of carbon-offset payments. In this research in progress, we describe the research background and a prototypical online environment we developed to conduct a series of online experiments with a variety of “nudges” to promote environmentally friendly decisions. We present the results of an experiment with 150 participants, which show that proposing higher levels of default payments (presented as a slide bar) on an online flight-booking platform significantly increases the amount of carbon-offset payments. Our research contributes to the emergent body of knowledge on green information systems and behavioural economics in IS and has important practical implications, as the results may help airlines and travel agents design online flight-booking processes such that more people decide in favour of offsetting the carbon emissions caused by their air travel.