### - o -

- OBJECT_HQ : object_type.h
- OBJECT_LIGHTHOUSE : object_type.h
- OBJECT_OWNED_LAND : object_type.h
- OBJECT_STATUE : object_type.h
- OBJECT_TRANSMITTER : object_type.h
- OPENTTD_GRAPHICS_BASE_GRF_ID : newgrf_config.cpp
- origin_currency_specs : currency.cpp
- ORIGINAL_BASE_YEAR : date_type.h
- ORIGINAL_END_YEAR : date_type.h
- ORIGINAL_MAX_YEAR : date_type.h
- ORIGINAL_SAMPLE_COUNT : sound_type.h
- OSK_KEYBOARD_ENTRIES : textbuf_gui.h
- OUTPUT_BLOCK_SIZE : settingsgen.cpp
- OwnedPPPonPCP : elrail_data.h