This is the dataset to accompany the International Journal of Greenhouse Gas Control manuscript entitled: Using oxygen isotopes to quantitatively assess residual CO2 saturation during the CO2CRC Otway Stage 2B Extension residual saturation test by Serno et al., published in 2016 http://dx.doi.org/10.1016/j.ijggc.2016.06.019. The data was collected at the CO2CRC Otway test site in December 2014, processed in Edinburgh and is now presented as an excel file.