The attached data files underpin the publication “The characteristics of billows associated with internal solitary waves”. The following file types and formats are included: Fig_#_movie.avi: Movie of experiment corresponding to fig_# in manuscript piv_####.dfi: PIV output from DigiFlow (DigiFlow software needed to view) piv_####.jpg: PIV output converted to jpg #######.TXT: Text file of probe data, 1st column corresponds to depth and subsequent columns to conductivity measurements. exp_index_oslo.xls: Index of experimental data (read with excel) exp_thorpe_scales.xls: Index of experimetal Thorpe scale calculations (read with excel) index.ods - spreadsheet detailing numerical parameters that were run in simulations (read with excel). interwv.tar.gz - zipped file containing source code (in Fortran 90) to run numerical simulations.