This type of credit represents one tonne of CO₂ or other greenhouse gases that are reduced, removed or saved. Critics say these certificates are used as a cheap way to fulfil climate promises to investors.

UK-listed oil companies Shell and BP have scaled back their spending on clean energy in the past year. The voluntary carbon market runs alongside larger and more expensive trading schemes run by governments, including the EU Emissions Trading Scheme, under which polluters trade allowances that give them the right to emit.

"Set-aside credits"

Shell uses credits to meet some of its climate pledges, including a target to reduce emissions per unit of energy sold by 15 to 20 per cent by the end of the decade compared to 2016.

To be used as offsets, credits must first be "retired", meaning they cannot be traded further, so the saving can only be counted once.

MSCI Carbon Markets, whose data for the past year covers major platforms that issue carbon credits, said Shell retired 14.9 million credits from global trading in 2024, more than twice as many as Italian power producer Eni, the next largest buyer. Separate data shows Shell withdrew almost three times as many credits as the next most prominent user, Microsoft, last year, consultancy Allied Offsets tells the Financial Times.

Voluntary carbon markets: suspected fraud

"We are withdrawing credits to offset emissions, including those associated with the energy our customers use in transport, homes, manufacturing goods and providing services," Shell says of the new data.

It adds that "decarbonisation must start with avoiding and reducing emissions", but that carbon credits could "offset" emissions where it is not possible to swap technologies for zero-emission alternatives quickly enough.

Voluntary carbon markets outside the jurisdiction of governments have been rocked by allegations of fraud, double counting, abuse of indigenous communities and flawed methodologies. Since then, energy companies have suspended some of their purchases of new allowances, says Dirk Forrister, executive director of the International Emissions Trading Association, a Swiss-based lobby group. But they have used up their old stock of credits and counted them towards the climate targets.

In contrast, tech companies such as Microsoft have announced that they will continue to sign new contracts in the coming years to offset their AI-based emissions.