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Abstract The isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios in dissolved oxygen. To improve our understanding of oxygen cycling in the ocean's interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2‐D isotopologue‐enabled isopycnal reaction‐transport model. We measured¹⁸O/¹⁶O and¹⁷O/¹⁶O ratios, as well as the “clumped”¹⁸O¹⁸O isotopologue in the northeast Pacific, and compared the results to previously published data. We find evidence that oxygen consumption in the northeast Pacific follows different mass‐dependent fractionation exponents from those typically used in oceanographic studies. These fractionation factors imply that an elevated proportion of¹⁷O compared to¹⁸O in dissolved oxygen—that is, its triple‐oxygen isotope composition—may not uniquely reflect only gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed.