UPDATE 2-Exxon sees nat gas passing coal demand by 2030

* Gas to overtake coal as No. 2 fuel by 2030

* Global energy demand to rise 25 pct from 2005

* Energy demand to be driven by developing economies (Adds details, forecast for renewables)

NEW YORK, Jan 27 (Reuters) - Natural gas will surpass coal as the second-largest global energy source behind oil by 2030, even as overall global demand for energy jumps 35 percent from 2005 levels, oil company Exxon Mobil (XOM.N) said on Thursday.

That energy demand will be fastest in developing economies, where usage will climb 70 percent, while developed economies will see essentially flat demand because of improvements in energy efficiency, Exxon, the world's largest publicly traded company said in its annual energy outlook.

New supplies of gas, including the shale rock fields that are now being tapped across North America, and its lower environmental impact versus other fuels, will drive that higher demand.

Exxon and its peers such as Chevron (CVX.N) have invested heavily in large natural gas developments in recent years.

Power generation is the fastest growing major energy-demand sector, the company said, and will contribute 55 percent of the total growth in demand through 2030, bringing its share of total energy demand to 40 percent.

Alternative sources of energy such as wind, solar and biofuels will grow about 10 percent per year through 2030, but will still contribute only about 2.5 percent of total global energy supplies, Exxon said. (Reporting by Matt Daily; Editing by Derek Caney and Maureen Bavdek)