Some big oil companies say they want to play a key role in reducing carbon emissions, but they are set to be sidelined at the coming United Nations climate conference.

Retailers, tech companies and consumer products makers have all been named as “principal partners” for COP26 in Glasgow—allowing them greater involvement with the event—but major oil companies like BP BP -1.62% PLC and Royal Dutch Shell PLC will have a lower profile. That is because the oil industry has yet to agree on science-based plans for how it will reduce carbon emissions, a hurdle U.K. organizers set as a prerequisite for involvement in the event.

Companies that haven’t set out credible emissions-reduction plans, as determined by a U.N.-backed third party, are unable to sponsor the event, run workshops and panel discussions, or book exhibition space in areas managed by the U.K. government.

“The COP26 Presidency is working most closely with organizations that are committed to taking real, positive action and have strong climate credentials,” a COP26 spokesman said. COP, which stands for conference of the parties, is the U.N.’s flagship annual climate event, and this year the U.K. is in charge of organizing it as the host country.

While the main focus of the meeting, which starts in Glasgow on Oct. 31, will be climate negotiations between governments, businesses have sought to engage with the event as they see both the risks and commercial opportunities of climate change.

BP and Shell officials are disappointed at being sidelined, people familiar with the matter said.

PHOTO: CHRISTOPHER M. MATTHEWS/THE WALL STREET JOURNAL

Fossil-fuel companies have sometimes sponsored previous COP meetings, particularly when hosted in their home country, but their association drew criticism from environmental groups.

Officials at BP and Shell, which are both listed in London and have a large presence in the U.K., are disappointed at being sidelined at the event, people familiar with the matter said. Both companies had hoped to be involved, the people said, having set out plans to pivot away from oil and gas and invest more in low-carbon energy. The sidelining of the industry is seen as less important to U.S. rivals Exxon Mobil Corp. and Chevron Corp. because they have a smaller presence in Britain.

“COP26 is primarily for governments—we want it to be a success and stand ready to support the efforts of the U.K. government and other governments around the world in whatever way we can,” said a BP spokeswoman.

Oil companies still plan to send staff to COP and BP said Chief Executive Bernard Looney plans to attend. Company representatives can, as members of industry groups, attend the event as observers, which is how many business people go.

Shell said its “focus is on what can be achieved through the momentum leading up to COP26 and beyond.”