The heads of Europe’s largest oil and gas companies called for governments to agree to carbon pricing at a United Nations-led summit on climate change in Paris at the end of the year.

“We urge governments to take decisive action at December’s UN summit,” the chief executive officers of six energy companies wrote in a letter published on Monday in the Financial Times. “We are also united in believing such action should recognize the vital roles of natural gas and carbon pricing in helping to meet the world’s demand for energy more sustainably.”

The banding together on climate-change policy by BP Plc, Eni SpA, Royal Dutch Shell Plc, Total SA and BG Group Plc is unprecedented and follows comments by some of their CEOs in recent months calling for the industry to be part of the debate on a deal limiting greenhouse gases.

The letter promotes natural gas as the least-polluting of fossil fuels and coincides with the start of the World Gas Conference in Paris this week.

“We write to highlight the major role natural gas can play in addressing climate change,” the CEOs wrote in the letter. “We believe the pragmatic step of implementing a widespread and effective pricing of carbon emissions is critical to realizing the full and positive impact natural gas can have.”

Carbon pricing was the main theme of a meeting last month - - also in Paris -- of business leaders on climate change during which CEOs from the banking, insurance and consumer products industries as well as energy called for a cost to be placed on carbon emissions as an incentive for companies and countries.

For their part, the biggest U.S. oil producers have rejected the common stance of their European counterparts. Exxon Mobil Corp. CEO Rex Tillerson said he doesn’t intend to “fake it.”

“We don’t intend to participate in that coalition,” Chevron Chairman and Chief Executive Officer John Watson told investors. “We think we can make our statements, and our statements speak for themselves.”

Emissions data released through the Carbon Disclosure Project show little difference between the U.S. and European oil companies over the past four years. All have reduced pollution “slightly” since 2011, with BP in the lead mainly because of asset sales needed to pay more than $40 billion in costs associated with the Gulf of Mexico disaster in 2010.