Open Access (OA) in scholarly publishing refers to the practice of providing unrestricted, free-of-charge access to scholarly research outputs—such as journal articles, conference papers, theses, and datasets—via the internet. The core aim of OA is to make research findings universally and immediately available to anyone, anywhere, without the financial, legal, or technical barriers typically associated with traditional subscription-based journals. For example, a researcher in a developing country without access to expensive databases can still read a freely available article published in an OA journal like PLOS ONE or BMC Public Health.
By removing paywalls and licensing restrictions, Open Access facilitates broader dissemination, increased visibility, and greater citation impact of scholarly work. This accessibility helps support academic collaboration across institutions and borders, especially where funding and access are limited. Green OA allows authors to deposit preprints or postprints in repositories like arXiv, PubMed Central, or institutional repositories such as Harvard DASH. In contrast, Gold OA involves publishing in journals where the final version of the article is openly available on the publisher’s website, often under Creative Commons licenses (e.g., CC BY), such as with journals from Frontiers or MDPI.
OA is increasingly supported by universities, governments, and funding bodies like the European Commission and the Bill & Melinda Gates Foundation, which mandate open access to publicly funded research. This growing support reflects the global shift toward more transparent, inclusive, and equitable systems of knowledge dissemination, helping ensure that science and scholarship benefit not just the few, but all.
Main Types of Open Access Models in Scholarly Publishing
Open Access (OA) has transformed scholarly publishing by removing traditional paywalls and making research outputs freely available to a global audience. Over the years, several OA models have emerged, each with distinct approaches to accessibility, funding, and licensing. Understanding these models is essential for researchers, institutions, and policymakers seeking to maximize the visibility and impact of academic work. The main types of Open Access models are discussed below.
1. Green Open Access (Self-Archiving):
Green Open Access, also known as self-archiving, is one of the most cost-effective and widely adopted approaches to making scholarly research freely available. Under this model, authors deposit a version of their manuscript in an open-access repository, allowing readers to access the work without subscription fees. These repositories may be institutional, maintained by universities or research organizations; discipline-specific, serving particular subject areas; or general-purpose platforms that accept research from all fields. The version deposited can vary depending on the publisher’s policy. In some cases, authors may share a preprint, which is the version submitted before peer review, while others may allow a postprint or Author Accepted Manuscript (AAM), which incorporates peer-review feedback but lacks the publisher’s formatting. In rare instances, the final published PDF may be deposited, though this is often restricted.
Many publishers enforce embargo periods before a deposited work can be made openly available. These periods, which vary by journal and discipline, typically range from a few months to several years. For example, biomedical research often has shorter embargoes due to funder requirements for rapid access, while humanities publications may have longer waiting times. Licensing terms also differ across publishers, with some allowing open licenses, such as Creative Commons, to enable broader reuse, and others limiting access to read-only formats. Well-known examples of Green OA repositories include Harvard DASH, MIT DSpace, and the Oxford Research Archive at the institutional level; subject-focused archives like arXiv for physics and mathematics, PubMed Central for biomedical sciences, and SSRN for social sciences; and general-purpose platforms such as Zenodo and Figshare.
The benefits of Green OA are significant. It is typically free for both authors and readers, increases the visibility and citation potential of research, ensures compliance with many funder mandates, and provides long-term archiving and preservation of scholarly work. However, it also comes with limitations, such as the possibility of version confusion when multiple versions of a work are available, embargo-related delays that can affect timely dissemination, and restrictive licensing terms set by some publishers. Despite these challenges, Green Open Access remains an important and practical route for researchers to share their findings widely, comply with open access requirements, and contribute to the global movement toward equitable access to knowledge while still publishing in traditional subscription-based journals.
2. Gold Open Access:
Gold Open Access is a publishing model in which the final, peer-reviewed version of a scholarly article is made freely and immediately available to readers on the publisher’s website. Unlike subscription-based journals, Gold OA ensures that there are no paywalls or access restrictions, allowing anyone to read, download, and share the content from the moment it is published. In most cases, the articles are distributed under open licenses—commonly Creative Commons licenses such as CC BY—which grant users broad rights to reuse, adapt, and redistribute the work with proper attribution. This model is typically funded through Article Processing Charges (APCs), which are paid by the author, their institution, or a research funder to cover publication and editorial costs. The amount of the APC varies widely depending on the publisher and journal prestige, ranging from a few hundred to several thousand US dollars.
Gold OA journals operate across all disciplines and may be managed by commercial publishers, scholarly societies, or non-profit organizations. Examples of well-known Gold OA publishers and journals include PLOS ONE, BMC Biology, Frontiers in Psychology, and PeerJ. One of the major advantages of Gold OA is the immediate visibility it provides, which can lead to higher readership and citation rates. Furthermore, because the Version of Record is openly available, readers have access to the fully formatted, copyedited, and citable version of the work. This supports academic transparency, facilitates knowledge sharing, and enables faster dissemination of research findings, which is particularly valuable in fields where timely access to new information is critical, such as medical research or environmental studies.
Despite its benefits, Gold OA also has some challenges. The reliance on APCs can create financial barriers for authors from institutions or countries with limited research funding, potentially leading to inequalities in who can publish. In response, some Gold OA publishers offer fee waivers or discounts for researchers from low- and middle-income countries. Additionally, the growth of predatory journals—unethical publishers that exploit the APC model without providing proper peer review—has raised concerns about quality control in the OA landscape. Nonetheless, when managed by reputable publishers, Gold Open Access remains one of the most effective and transparent ways to make research outputs widely accessible, supporting the global movement toward open science and equitable knowledge dissemination.
3. Diamond (or Platinum) Open Access:
Diamond, also known as Platinum Open Access, is a publishing model in which scholarly works are made freely available to readers without charging either subscription fees or Article Processing Charges (APCs) to authors. This model removes financial barriers for both producers and consumers of research, making it one of the most equitable forms of Open Access. Funding for Diamond OA publications typically comes from academic institutions, research organizations, scholarly societies, government grants, or philanthropic contributions. In many cases, these journals are run by non-profit entities or volunteer editorial teams who are committed to promoting open scholarship and advancing knowledge dissemination without commercial motives.
In Diamond OA, the final, peer-reviewed, and fully formatted version of the work is published openly on the journal’s website, often under a Creative Commons license such as CC BY, which enables broad reuse, adaptation, and redistribution with proper attribution. Since there are no APCs, this model is particularly beneficial for researchers from low- and middle-income countries or institutions with limited funding, ensuring their work can be published without financial strain. Notable examples of Diamond OA journals include the Journal of Machine Learning Research (JMLR), SciPost Physics, and many university- or society-based publications in the humanities and social sciences.
One of the key advantages of Diamond OA is its strong alignment with the principles of equity, inclusivity, and public good in scholarly communication. It eliminates the pay-to-publish barrier that exists in some Gold OA models while maintaining the benefits of immediate access, wide dissemination, and increased citation potential. However, sustaining this model can be challenging, as it relies heavily on stable institutional support, volunteer labor, and long-term funding commitments. Without consistent financial backing, Diamond OA journals may struggle to cover operational costs such as editorial management systems, copyediting, and website maintenance. Nevertheless, this model is gaining increasing attention in policy discussions about the future of Open Access, as it offers a sustainable and fair approach to academic publishing that benefits the entire research community.
4. Hybrid Open Access:
Hybrid Open Access is a publishing model offered by subscription-based journals in which authors can choose to make their individual articles freely and immediately available to readers by paying an Article Processing Charge (APC). In this model, the journal continues to operate primarily on a subscription basis, meaning that most of its content remains behind a paywall, while only the articles for which authors have opted to pay the APC are openly accessible. This approach allows authors who require or prefer Open Access—often due to funder mandates or institutional policies—to publish in well-established, high-impact subscription journals while still meeting open accessibility requirements. The openly available articles are typically published under a Creative Commons license, most commonly CC BY, allowing for broad reuse with proper attribution.
While Hybrid OA offers flexibility and allows authors to publish in prestigious journals without compromising on access requirements, it has been criticized for its potential to create inefficiencies in the publishing system. A major concern is the issue of “double dipping,” where publishers receive payment both from subscriptions and from APCs for the same journal, without necessarily reducing subscription fees in proportion to the number of OA articles published. This has led many libraries, funding agencies, and policy groups to question the cost-effectiveness of supporting Hybrid OA. As a result, some funders, such as those aligned with Plan S, have stated that they will no longer cover APCs for Hybrid OA unless the journal has a clear transition plan toward full Open Access.
Despite these criticisms, Hybrid OA remains a significant part of the scholarly publishing landscape. It can serve as a transitional model for journals moving from subscription-based to fully Open Access publishing, and it provides authors with more publishing options in fields where reputable fully OA journals are limited. Well-known examples of Hybrid OA programs include Elsevier’s “Open Access Articles” option, Wiley’s “OnlineOpen,” and Springer Nature’s “Open Choice.” For researchers aiming to combine the reach of Open Access with the prestige of selective journals, Hybrid OA offers a viable—though often costly—pathway.
5. Bronze Open Access:
Bronze Open Access is a form of open availability in which scholarly articles are made free to read on the publisher’s website but do not carry a clearly stated open license, such as a Creative Commons license. This means that, while the content is accessible without payment, the rights for reuse, redistribution, or adaptation are unclear and typically remain restricted under traditional copyright. As a result, Bronze OA differs from other Open Access models—such as Gold, Diamond, or Green OA—which explicitly grant users certain freedoms for reusing the work. In many cases, Bronze OA is offered temporarily, often as part of promotional campaigns, public interest initiatives, or special collections related to current events. For example, during global health crises like the COVID-19 pandemic, many publishers made selected research articles free to read to ensure rapid access to critical information, but without granting long-term reuse rights.
The main advantage of Bronze OA is that it expands the immediate readership of scholarly works, particularly when publishers release high-impact articles or issues to the public without subscription barriers. This can increase visibility, citations, and the broader dissemination of knowledge in the short term. However, the lack of explicit licensing limits its long-term value for open scholarship, as researchers, educators, and policymakers may be unable to legally reuse or adapt the content. Furthermore, because Bronze OA availability often depends on publisher discretion, access can be revoked at any time, turning previously free articles back into paywalled content. This uncertainty makes Bronze OA less reliable as a sustainable access model compared to other OA types.
In practice, Bronze Open Access is often seen as a halfway measure between full Open Access and traditional subscription publishing—useful for immediate visibility but insufficient for advancing the principles of open science in the long run. While it plays a role in widening short-term access, especially during times of urgent need, its temporary nature and unclear rights framework mean that it cannot substitute for fully licensed and permanent Open Access models.
6. Delayed Open Access:
Delayed Open Access is a publishing model in which scholarly articles are initially placed behind a paywall and made accessible only to subscribers or paying readers, but become freely available to the public after a predetermined embargo period set by the publisher. This embargo period typically ranges from six months to two years, depending on the discipline, journal policy, and publisher requirements. For example, many biomedical and life sciences journals impose shorter embargo periods of around 6–12 months to comply with funding mandates for timely dissemination, while journals in the humanities and social sciences may have longer delays. Once the embargo period expires, the final published version of the article is made openly accessible on the publisher’s platform, often without an explicit open license, which can limit reuse rights.
The main purpose of Delayed Open Access is to balance the publisher’s need for subscription revenue with the academic community’s demand for wider access to research. It allows publishers to monetize the initial period of exclusivity for subscribers while eventually contributing to the open dissemination of knowledge. This model is common among traditional subscription-based journals, such as certain titles from Oxford University Press and Cambridge University Press, as well as some society-led publications.
While Delayed OA increases long-term access to scholarly work, it has notable limitations. The embargo period can hinder the timely sharing of research, which is particularly problematic in fast-moving fields like medicine, climate science, or technology, where immediate access to findings is critical. Additionally, the lack of open licensing in many delayed OA releases means that while readers can freely access the content, they may not have the rights to reuse or adapt it for educational or derivative works. Despite these challenges, Delayed Open Access remains a compromise model that expands access over time and can help bridge the gap between fully paywalled content and immediate Open Access publishing.
Open Access models vary in terms of cost, accessibility, and licensing, offering different pathways for authors to share their work with the global community. While Green and Gold OA remain the most widely recognized, emerging models like Diamond OA are gaining traction as sustainable, equitable alternatives. Understanding these models helps researchers choose the most suitable publication route based on their funding situation, discipline, and dissemination goals.
