O'Connor and Walker 1993
Oken 1815
Olaru 1978a
Olaru 1978b
Oleinik 1975
Oleinik 1976
Olsson and Youssefnia 1979
Osorio Tafall 1942
Ostenfeld 1903
Ostenfeld and Nygaard 1908
Ostenfeld and Nygaard 1925
Ostenfeld and Schmidt 1901
Ouyang Shu 1979