By 2030, natural gas will have become the second-largest global energy source -- ahead of coal -- aided by technologies that have unlocked enormous new supplies of gas from shale, tight formations and coalbed methane, ExxonMobil Corp. said Thursday.

ExxonMobil's "Outlook for Energy: A View to 2030" is part of the supermajor's annual predictions regarding global energy supplies. The company has a big stake in the future of unconventionals as the largest U.S. gas producer and one of the biggest shale producers after buying XTO Energy Corp. in late 2009.

The market share of coal will decline over the next 20 years, particularly in developed global countries, natural gas "will continue to play a key role through 2030 and beyond," researchers said. The growth of natural gas "both in its application across sectors, as well as in the quantity of available, affordable supplies is a prime example of how technological advances have enabled energy sources to adapt to the world's changing needs."

The changes in energy use and technology development "reflect an evolutionary process that spans decades," said the report. "Over time, however, the process leads to revolutionary impacts."

Recent technology advances have "unlocked vast resources of shale gas in North America, expanding opportunities for developed and developing nations to capture the benefits of gas as a reliable, affordable energy source that will also help support environmental improvements," the authors said. "These advances are part of the evolution that is contributing to the growth of gas as a key fuel source globally."

Unconventional gas is the fastest-growing source of global gas supply, said the report. New technologies, including horizontal drilling and hydraulic fracturing, "are safely expanding supplies" around the world.

"Globally, unconventional gas production is projected to grow fivefold from 2005 to 2030. The largest growth by far is in the United States, where unconventional production meets well over half of U.S. gas demand by 2030."

In 2005, noted ExxonMobil, domestic conventional gas made up about 80% of total supplies. However, by 2030, "that share declines to about 60%, with unconventional gas and imports supplying the remainder." U.S. gas resource estimates have increased 35% "in just the last two years."