Comparison of ¹⁷O/¹⁶O and ¹⁸O/¹⁶O ratios in AGB stars with those derived in oxide pre-solar grains of type I (gray dots) and II (gray squares) as defined by Nittler et al. (1994), taken from the database http://presolar.wustl.edu. As Fig. 1, color symbols are the AGB carbon stars analyzed here. Open black circles: O-rich AGB stars of types M, MS and S from Smith & Lambert (1990); solid black circles: O-rich Miras from Hinkle et al. (2016). Error bars in the pre-solar grains are smaller than the symbol size. Note the logarithmic scale.