Global energy demand will rise by 25 percent through 2040, but greater use of low-carbon fuels will cut carbon emission relative to economic activity, said an ExxonMobil forecast released Monday.

The petroleum giant said oil will still be the biggest source of energy in 2040, but natural gas will move into second place, as use of coal ebbs in response to tighter regulations on carbon dioxide.

The shifts will enable the global economy to cut in half its "carbon intensity," a benchmark of carbon emissions to economic activity, the report said.

"Energy efficiency gains are expected to be a major contributor to this achievement, supported by a gradual but significant transition to less-carbon-intensive energy types," the report said.

About 40 percent of the growth in energy demand through 2040 will come from nuclear and various renewable technologies, including bio-energy, hydro, geothermal, wind and solar, according to the forecast.

By contrast, overall coal use is projected to fall, with the share of electricity from coal dropping to 30 percent in 2040 from 40 percent in 2014.

"The climate accord reached at the recent COP 21 conference in Paris set many new goals, and while many related policies are still emerging, the outlook continues to anticipate that such policies will increase the cost of carbon dioxide emissions over time," said William Colton, vice president of ExxonMobil corporate strategic planning.

Driving the increase in overall energy use will be a growth of two billion in the global population to nine billion in 2040.

ExxonMobil projected global carbon dioxide emissions will peak around 2030 and then start to decline. China's emissions also peak in 2030 before dropping off.

However, emissions in India and some other emerging economies are seen increasing through the entire period.

Those gains are offset elsewhere. Emissions in wealthier countries in the Organization for Economic Cooperation and Development will fall about 20 percent from 2014 to 2040.