O

1. Office in home
2. Oil and gas wells:
3. Oil and gas wells:   Depletion
4. Oil and gas wells:   Drilling costs
5. Oil and gas wells:   Partnerships
6. Oil and gas wells:   S corporations
7. Optional method:
8. Optional method:   Farm
9. Optional method:   Nonfarm
10. Optional method:   Reasons to use
11. Options, dealer in
12. Ordinary expense
13. Ordinary gain or loss
14. Ordinary or capital gain
15. Organization costs
16. Organization costs:   Corporate
17. Organization costs:   Partnership
18. Organization expenses
19. Original issue discount
20. Orphan drug credit
21. Other deductible expenses
22. Other nondeductible expenses
23. Outplacement services