Omma Centre of Contemporary Art
- Mediator between artists and art buyers, as well as between artists and galleries.
- http://www.omma.us

One Of A Kind Paintings
- A fine art collection of antique and vintage American and European paintings, modern, abstract expressionist, impressionist, oils on canvas - drawings and charcols- oil on board and watercolors from the 18th 19th and 20th century periods.
- http://www.oneofakindantiques.com/paintings/

Outer Borough
- An online art space offering prints, paintings, drawings and collectible vinyl toys by emerging, contemporary and street artists.
- http://www.outer-borough.com/

OmniFineArt
- Fine art reproductions on canvas print, Smithsonian reproductions, museum reproductions, original sculpture and contemporary paintings.
- http://www.omnifineart.com/

Online Graphics Art Gallery
- They exhibit computer art from freehand drawings, Photoshop and Bryce 3D images, and photographs. They offer limited edition prints, artistic business cards and web design services.
- http://www.imagelair.com/

Outsider's Gallery
- Works organized in groupings by artist.
- http://www.outsidersgallery.com

One World Art
- Offers image prints and original paintings by various artists.
- http://1worldart.com

Original Paintings For Sale
- They offer a variety of original paintings and prints.
- http://www.originalpaintingsforsale.com/

Offer Waterman & Co.
- Located in London, they buy paintings from Sotheby's, Christie's, Bonham's, Phillip's privately and specialise in mordern British painting.
- http://www.waterman.co.uk

OnsiteArt Gallery
- Lithographs, original paintings and watercolors, serigraphs, mixed media and etchings.
- http://www.onsiteart.com

Outer Most Arts Gallery
- Representing painters, printmakers, sculptors and photographers.
- http://www.outermostarts.com/