Oceano Azul Foundation in Portugal works to contribute to the conservation and sustainable use of the ocean. They operate in close partnership with Oceanario de Lisboa

Oceanologico conducts interdisciplinary research in the fields of marine biodiversity, environmental pollution (microplastics) and the relationship between humans and the ocean on the island of La Palma in the Canarian Archipelago. They also conduct snorkelling and diving tours and have an overall aim of improving ocean literacy generally.

Oceanomare-Delphis research and monitor cetaceans in the Mediterranean, with aim of conserving cetaceans and marine biodiversity. The focus is on non-invasive studies, promoting education and conservation programmes and enhancing public awareness of, and concern for, cetaceans and the marine environment. ODO advocates for financial support of scientific and conservation programmes and facilitates dissemination of results through professional networking, capacity building, public outreach and scientific publications. The organisation believes the application of scientific knowledge to management and policy is essential for effective cetacean conservation. The Ischia Dolphin Project is one of their many initiatives.

Oceanosanos is a campaign created by the OCC (Cetacean Conservation Organization) in Uruguay to inform citizens about the threat to marine biodiversity of the current fishing model and to create propositional actions. They work 'to strengthen sustainable fishing, create marine reserves and combat ocean problems'.

Oceans Alive Conservation Trust's statement of their work: 'Scientific research, collaboration, protection, rehabilitation, conservation, community awareness education, social upliftment and a call to action is at the heart of everything we do to ensure a healthy and sustainable future for our oceans and our coastal environments for all future generations'.

With offices in Ottawa, Winnipeg and Halifax, Oceans North supports marine conservation in partnership with Indigenous and coastal communities. Their science- and community-based conservation in the Arctic regions of Canada and Greenland has the goal to promote policies and programs that address the unprecedented environmental changes taking place in the North and ensure that its waters are protected within the framework of Inuit knowledge, rights and consultation.

Oceans Research specialises in investigating the biology and ecology of mega-fauna, including sharks, marine mammals and terrestrial carnivores. They advise governmental and non-governmental bodies on relevant conservation issues.

Oceans 5 is an international marine funders collaborative focused on ending overfishing, establishing marine reserves and combating illegal fishing. Founded in 2011 by four philanthropic institutions, it now includes 15 Partners and Members, providing about $12 million annually in grants to organizations working in all five oceans. In the past nine years, Oceans 5 grantees have achieved remarkable successes, including establishing several of the world’s largest fully protected areas and securing significant new fisheries conservation policies in the United States, European Union and Japan.

Octonation aims at informing the public about octopuses.

The Octopus Foundation is a Swiss non-profit organization that aims to improve the knowledge of the marine world by supporting scientific exploration of the oceans and to make this information available to the public. Amongst projects supported are several involving the conservation of marine life (monk seals, seahorses, and turtles, all in the Mediterranean) and several involving marine archaeology.

The One Ocean Hub is a global consortium of researchers aiming to bridge the disconnect between law, science, policy and art to support sustainable management of the marine environment. Lasting 2019-2024 and funded by UK Research and Innovation (UKRI) through the Global Challenges Research Fund (GCRF), the intention is to inform aid strategies and research in achieving the United Nations Sustainable Development Goals. The Hub is focusing its efforts on addressing issues in South Africa, Namibia, Ghana, Fiji and The Solomon Islands. These are all developing nations which rely heavily on the ocean for resources to meet their economic development goals, thus sustainable fishing is a significant part of the programme.

Operation Wallacea is a biodiversity and climate research organisation. For 25 years it has run biodiversity field expeditions to support the research of hundreds of academics and funded from tuition fees paid by students that then gain experience of working with publishing scientists. Opwall is at centre of a small network of organisations. The conservation projects are often run through the Wallacea Trust), whilst Wildlife Experience tours at the Opwall research sites and outside the main Opwall research season are run by a sister organisation – Friends of Wallacea . Expeditions in the marine field include projects such as a coral reef conservation in Madagascar, and coral reef and turtle conservation in Mexico.