The oxygen isotopic ratio
18O/
16O has been measured in cometary gas for a wide variety of comets, but it has only been measured in cometary dust by Stardust. Most such measurements find a value of the ratio that is consistent with Vienna Standard Mean Ocean Water within errors. In this talk I will present the result of a measurement of the oxygen isotopic ratio in dust from Comet 67P/Churyumov-Gerasimenko with the COSIMA instrument aboard the Rosetta spacecraft. Measuring the
18O/
16O ratio with COSIMA is challenging for a number of reasons, but it is possible with a reasonable degree of precision.
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