•A novel, hand-collected and publicly available dataset on informal collaboration is sourced from 5631 acknowledgement sections.•Females are acknowledged by fewer papers and by fewer authors than comparable males.•The network of informal collaboration contains valuable information on author productivity and paper success that is currently not used.•Centrality in the network of informal collaboration constitutes a novel ranking of researchers. We present and discuss a novel dataset on informal collaboration in financial economics, manually collected from more than 5,000 acknowledgement sections of published papers. We find that informal collaboration is the norm in financial economics, while generational differences in informal collaboration exist and reciprocity among collaborators prevails. Female researchers appear less often in acknowledgements than comparable male researchers. Information derived from networks of informal collaboration allows us to predict academic impact of both researchers and papers even better than information from co-author networks. Finally, we study the characteristics of the networks using various measures from network theory and characterize what determines a researcher’s position in it. The data presented here may help other researchers to shed light on an under-explored topic.