This dataset contains the stable carbon isotope data used to calculate the range of coccolith δ13C vital effects over the past 60 million years (expressed as the difference between the d13C of small and large coccoliths), as plotted in Figure 4 of the review paper Coccoliths as Recorders of Paleoceanography and Paleoclimate over the Past 66 Million Years by Bolton & Stoll (2025, AREPS; doi:10.1146/annurev-earth-040623-103211). It is a compilation of previously published and unpublished data over the last 60 million years. The data provide insights into coccolithophore evolution, physiology, and adaptation to changing climate, of interest for paleoceanographic research. Data come from ODP/IODP, NGHP, and MD sediment cores from the Atlantic, Pacific and Indian Oceans, and are based on measurements of purified coccolith fractions made on an isotope-ratio mass spectrometer.