Oxman
- Worldwide single name study.
- http://www.littlewhitebull.com/oxman1/

Ottolenghi
- All family members regardless of country and relation. Includes spelling variants of Ottolenghi and Ottolangui.
- http://www.ottolenghi.org/

Oshel
- History, pedigree and application of the name.
- http://www.oshel.com/

Orrell Family Association
- Research repository for Orrell and variations, worldwide and all time periods.
- http://www.orrellfamily.com/

Orear
- Communication and information forum for O'Rears and Orears.
- http://www.orear.com/

Ollis
- Multinational family histories pertaining to the name Ollis including photographs, memorials, vital records and lineages during War.
- http://freepages.genealogy.rootsweb.com/~ollis/

Odell
- Starting point for research into the Odell name and its variants, with particular emphasis on UK roots.
- http://www.odells.info/ode_gene.html

Ogbourne Chronicles
- Historical information relating to the names and its variants in the UK and USA. Includes descendants of slaves owned by Charles Harrison Ogburn of Mecklenburg, Virginia.
- http://www.oginet.com/Chronicles/

Orton Archive
- Historical data, will abstracts, deeds and parish register entries relating to Reginald Orton 1810-1862. Includes British ancestors, Inman of Nidderdale, Bayles of Laxton, Peirse of Bedale, Wastell of Scorton and Hutton of Marske. Compiled by Nancy McLa
- http://freepages.history.rootsweb.com/~enzedders/

Olley
- Family history including associated lineages, message board and photographs.
- http://www.olley.org/

Olds Family
- Ancestral research featuring pedigree, photographs and resources. Includes the variants Oulds and Old.
- http://www.olds-family.com/

Oddy: Sandy's Family History
- Features ahnentafel chart and the surnames Oddy, Howes, Fincher and Plumley.
- http://sandys.50megs.com/

Overcast Family
- Ancestral heritage of Louis Overcast including associated lineages and links.
- http://www.overcastfamily.com/

Oliver-Velez
- Ancestors of Denise Roberts Oliver-Velez including the surnames Oliver, Velez, Roberts, Weaver, Williams, Bodine, and Bratt.
- http://www.wemba-music.org/ancestor.htm

Orlovac
- Descendants of Nikola Orlovac and Potomci od Nikole Orlovac including the lineages of Golub, Barisic and Lukenda from Bukovica. Compiled by Marinko Orlovac.
- http://familytreemaker.genealogy.com/users/o/r/l/Marinko-Orlovac/

Orzell
- Researching the family lines from Galicia to Connecticut and Vermont and throughout the USA.
- http://pages.cthome.net/orzell/

Oster
- Ancestors and descendants of Joseph Hickman Oster and Henrietta Marie Galliano as compiled by Brian Joseph Oster. Features the surnames Oster, Hickman, Galiano, Ledet and Kennedy. Includes abstracts of Missouri marriages and Louisiana obituaries.
- http://www.vienici.com/

Ossowski: Search
- Seeking information on Semyon Ionov Ossowski's relatives and those connected to the family blood line. Compiled by Alex Ossowski.
- http://ossowski.narod.ru/

Olive
- Ancestral heritage of Fred Olive from AL, USA.
- http://www.dpo.uab.edu/~folive/