The Kick Big Polluters Out coalition analysed the official lists of COP participants going back to 2003 and found that out of the thousands of accreditations affiliated with fossil fuel industries, 945 were directly linked to employees of oil and gas companies.

Major oil giants, including ExxonMobil, Chevron and Shell were granted "a minimum of 267 accreditations," according to a statement by the coalition.

The analysis comes just days ahead of COP28, hosted in Dubai and spearheaded by Sultan Al Jaber, also head of the United Arab Emirates' national oil company.

Sultan Al Jaber's designation for the COP presidency has been controversial, with proponents defending fossil fuel producers' right to participate in discussions aimed at reducing their use, and critics denouncing the active lobbying of oil and gas companies to water down negotiations.

Lobbyists from trade associations representing the world's biggest fossil fuel polluters also attended COP meetings at least 6,581 times over the timeframe.

"These groups have used their attendance at COP to lobby to advance fossil fuel interests," said the NGOs.

All COP delegates are required to be hosted by a government or admitted organisation, but lobbyists are passing "under the radar" by not declaring the fossil fuel firms they work for.

As a result, the figures likely "represent a significant undercount," said the coalition.

The last three COPs brought together around 22,000 people in Madrid, 38,000 in Glasgow and 49,000 in Sharm el-Sheikh. Prior to COP21, the number of participants ranged from 5,000-11,000, with the exception of COP15 (27,700).

The presence of lobbyists does not end with the fossil fuel industry, "other polluting industries deeply implicated in the climate crisis, such as finance, agribusiness, and transportation are also present," said the coalition, although their accreditations were not analysed.

But in an important step, COP28 will be the first talk to mandate the disclosure of participant affiliations.

"Civil society will be watching closely to determine exactly whether COP28 proves to be fossil fuel friendly or will instead prioritise people and the planet," said the authors.

The Kick Big Polluters Out coalition includes more than 450 groups such as Global Witness, Greenpeace, ActionAid and Transparency International.