Oxygen triple isotope measurements can be used to calculate aquatic gross oxygen production rates. Past stud-ies have emphasised the appropriate definition of the 17 O ex-cess and often used an approximation to derive production rates from the 17 O excess. Here, I show that the calculation can be phrased more consistently and without any approxi-mations using the relative 17 O/ 16 O and 18 O/ 16 O isotope ratio differences (delta values) directly. I call this the "dual delta method". The 17 O excess is merely a mathematical construct and the derived production rate is independent of its defini-tion, provided all calculations are performed with a consis-tent definition. I focus on the mixed layer, but also show how time series of triple isotope measurements below the mixed layer can be used to derive gross production. In the calculation of mixed layer productivity, I explicitly include isotopic fractionation during gas invasion and eva-sion, which requires the oxygen supersaturation s to be mea-sured as well. I also suggest how bubble injection could be considered in the same mathematical framework. I distin-guish between concentration steady state and isotopic steady state and show that only the latter needs to be assumed in the calculation. It is even possible to derive an estimate of the net production rate in the mixed layer that is independent of the assumption of concentration steady state. I review measurements of the parameters required for the calculation of gross production rates and show how their sys-tematic uncertainties as well as the use of different published calculation methods can cause large variations in the produc-tion rates for the same underlying isotope ratios. In particu-lar, the 17 O excess of dissolved O 2 in equilibrium with atmo-spheric O 2 and the 17 O excess of photosynthetic O 2 need to be re-measured. Because of these uncertainties, all calcula-Correspondence to: J. Kaiser (j.kaiser@uea.ac.uk) tion parameters should always be fully documented and the measured relative isotope ratio differences as well as the oxy-gen supersaturation should be permanently archived, so that improved measurements of the calculation parameters can be used to retrospectively improve production rates.