| O'Rourke, Joseph | Art Gallery Theorems and Algorithms | 05 Combinatorics |
| O'hEigeartaigh, M. | Combinatorial Optimization - Bibliography | 05 Combinatorics |
| Ockendon, Hilary | Inviscid Fluid Flows | 76 Fluid mechanics |
| Odlyzko, A.M. | Handbook of Combinatorics, Chapter 22: Asymptotic Enumeration Methods | 05 Combinatorics |
| Oehring, DePree | Elements of Complex Analysis | 30 Functions of a complex variable |
| Oleinik, Olga A. | Mathematical Problems Of Boundary Layer Theory | 35 Partial differential equations |
| Oleinik, O.A. | Second Order Equaitons With Nonnegative Characteristic Form | 35 Partial differential equations |
| Ollerenshaw, Kathleen | Most-Perfect Pandiagonal Magic Squares: Their Construction and Enumeration | 05 Combinatorics |
| Olmsted, John M. H. | Advanced Calculus | 26 Real functions |
| Olver, F | Asymptotics and Special Functions | 33 Special functions |
| Olver, F.W.J. | Asymptotics and Special Functions | 33 Special functions |
| Oprea, John | Differential Geometry and Its Applications | 53 Differential geometry |
| Orlik, Peter | Arrangements of Hyperplanes | 05 Combinatorics |
| Orlik, Peter | Introduction to Arrangements | 05 Combinatorics |
| Ortega, James M. | Numerical Methods for Differential Equations | 65 Numerical analysis |
| Ortega, James | Studies in Numerical Analysis II | 65 Numerical analysis |
| Osgood, William | Advanced Calculus | 26 Real functions |
| Osgood, William | Mechanics | 70 Mechanics of particles and systems |
| Osgood, William | Topics in the Theory of Functions of Several Complex Variables | 32 Several complex variables |
| Ovchinnikov, Sergei | Graphs and Cubes | 05 Combinatorics |
| Owen, Guillermo | Game Theory | 91 Game theory, economics, social and behavioral sciences |