| On the super replication price of unbounded claims Sara Biagini, Marco Frittelli | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the superselection theory of the Weyl algebra for diffeomorphism invariant quantum gauge theories Hanno Sahlmann, Thomas Thiemann | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the theory of system administration Mark Burgess | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the theta divisor of SU(2,1) Sonia Brivio, Alessandro Verra | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the tractable counting of theory models and its application to belief revision and truth maintenance Adnan Darwiche | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the use of expectations for detecting and repairing human-machine miscommunication Morena Danieli (CSELT - Turin, Italy) | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the use of non-canonical quantum statistics Jani Lukkarinen | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the utility of feature selection in building two-tier decision trees Sergey A. Saltykov | L4–5 Advanced | CC-BY-NC-ND | mirrored | 13 pp. | arxiv |
| On the variation of the Poisson structures of certain moduli spaces Johannes Huebschmann (Lille) | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the variety of rational space curves Z. Ran | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the von Neumann Inequality for Linear Matrix Functions of Several Variables Dmitriy S. Kalyuzhniy (Odessa, Ukraine) | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| On the Weakness of Short-Range Interactions in Fermi Gases Marcel Griesemer, Michael Hofacker | L4–5 Advanced | CC-BY-NC-ND | mirrored | 16 pp. | arxiv |
| On using Reproducible Hilbert Spaces for the analysis of Replicated Spatial Point Processes Amelia Sim\'o | L4–5 Advanced | CC-BY-NC-SA | mirrored | 20 pp. | arxiv |
| On weakly Tur\'an-good graphs D\'aniel Gerbner | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| On wonderful compactifications of $SL(2,F)$ for non-Archimedean local fields $F$ Corina Ciobotaru | L4–5 Advanced | CC-BY | mirrored | 16 pp. | arxiv |
| Open and closed complexity of infinite words O. Parshina, M. Postic | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Open Case Studies: Statistics and Data Science Education through Real-World Applications Carrie Wright, Qier Meng, Michael R. Breshock | L4–5 Advanced | CC-BY-NC-SA | mirrored | 25 pp. | arxiv |
| Open Data Quality Evaluation: A Comparative Analysis of Open Data in Latvia Anastasija Nikiforova | L4–5 Advanced | CC-BY | mirrored | 17 pp. | arxiv |
| Open Neuroscience Initiative Austin Lim | L1–3 Foundational | CC-BY-NC | mirrored | 413 pp. | libretexts |
| Open Signals and Systems Laboratory Exercises Andrew K. Bolstad & Julie A. Dickerson | L1–3 Foundational | CC-BY-NC | mirrored | 48 pp. | libretexts |
| Open Source Vizier: Distributed Infrastructure and API for Reliable and Flexible Blackbox Optimization Xingyou Song, Sagi Perel, Chansoo Lee | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Operational scheduling of oil products pipeline with intermediate event occurrences Seyyed Hamed Moghimi, Jafar Habibi, Hamid Jahad | L4–5 Advanced | CC-BY | mirrored | 20 pp. | arxiv |
| Opportunity Cost Algorithms for Combinatorial Auctions Karhan Akcoglu, James Aspnes, Bhaskar DasGupta | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Asset Allocation with Asymptotic Criteria Vladislav Kargin | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Belief Revision Carmen Vodislav, Robert E. Mercer | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Best Arm Identification in Two-Armed Bandits with a Fixed Budget under a Small Gap Masahiro Kato, Kaito Ariu, Masaaki Imaizumi | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal Bidding Algorithms Against Cheating in Multiple-Object Auctions Ming-Yang Kao, Junfeng Qi, Lei Tan | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Buy-and-Hold Strategies for Financial Markets with Bounded Daily Returns Gen-Huey Chen, Ming-Yang Kao, Yuh-Dauh Lyuu | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal control of stochastic delay differential equations and applications to path-dependent financial and economic models Filippo de Feo, Salvatore Federico, Andrzej \'Swi\k{e}ch | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal convergence rate for homogenization of convex Hamilton-Jacobi equations in the periodic spatial-temporal environment Hoang Nguyen-Tien | L4–5 Advanced | CC-BY | mirrored | 14 pp. | arxiv |
| Optimal Convergence Trading Vladislav Kargin | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Engagement-Diversity Tradeoffs in Social Media Fabian Baumann, Daniel Halpern, Ariel D. Procaccia | L4–5 Advanced | CC-BY-NC-ND | mirrored | 19 pp. | arxiv |
| Optimal geometric multigrid preconditioners for HDG-P0 schemes for the reaction-diffusion equation and the generalized Stokes equations Guosheng Fu, Wenzheng Kuang | L4–5 Advanced | CC-BY | mirrored | 35 pp. | arxiv |
| Optimal Impartial Correspondences Javier Cembrano, Felix Fischer, Max Klimm | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal index insurance and basis risk decomposition: an application to Kenya Matthieu Stigler, David Lobell | L4–5 Advanced | CC-BY-NC-ND | mirrored | 28 pp. | arxiv |
| Optimal intertemporal risk allocation applied to insurance pricing Kei Fukuda, Akihiko Inoue, Yumiharu Nakano | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Investment Horizons Ingve Simonsen, Mogens H. Jensen, Anders Johansen | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Investment in a Dual Risk Model Arash Fahim, Lingjiong Zhu | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal Investment in a Large Population of Competitive and Heterogeneous Agents Ludovic Tangpi, Xuchen Zhou | L4–5 Advanced | CC-BY-NC-ND | mirrored | 34 pp. | arxiv |
| Optimal Investment Strategy for Risky Assets Sergei Maslov, Yi-Cheng Zhang | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal Investment Strategy to Minimize Occupation Time Erhan Bayraktar, Virginia R. Young | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal investment with insurable background risk and nonlinear portfolio allocation frictions Hugo E. Ramirez, Rafael Serrano | L4–5 Advanced | CC-BY | mirrored | 25 pp. | arxiv |
| Optimality of threshold strategies for spectrally negative Levy processes and a positive terminal value at creeping ruin Chongrui Zhu | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimality of Universal Bayesian Sequence Prediction for General Loss and Alphabet Marcus Hutter | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal lag in dynamical investments M. Serva (Dip. di Matematica, I.N.F.M., Universit\`a dell'Aquila | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal long term investment model with memory Akihiko Inoue, Yumiharu Nakano | L4–5 Advanced | Licence unknown | link only | — | arxiv |
| Optimal management of DB pension fund under both underfunded and overfunded cases Guohui Guan, Zongxia Liang, Yi Xia | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal measure preserving derivatives revisited Brendan K. Beare | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal Mix Among PAYGO, EET and Individual Savings Lin He, Zongxia Liang, Zhaojie Ren | L4–5 Advanced | arxiv-nonexclusive | link only | — | arxiv |
| Optimal Myopic Attacks on Nonlinear Estimation R. Spencer Hallyburton, Amir Khazraei, Miroslav Pajic | L4–5 Advanced | CC-BY | mirrored | 6 pp. | arxiv |