Canada's Americas Petrogas Inc. (APEOF, BOE.V) said Friday that Exxon Mobil Corp. (XOM) has agreed to invest as much as $76.3 million to jointly explore for unconventional oil and gas in Argentina.

Exxon will invest $53.9 million for exploration and $22.4 million if the companies proceed to the exploitation phase, America Petrogas said in a statement.

In exchange, Exxon will gets a 45% stake in the project, with Americas Petrogas retaining 45% and the provincial oil and gas company, Gas y Petroleo del Neuquen, 10%.

Americas Petrogas shares traded on the Toronto Stock Exchange were recently up 29% at $2.19 Canadian dollars (US$2.24), but still down from their 52-week high of C$2.99.

The deal highlights rapidly growing interest in potentially vast unconventional oil and gas resources in hydrocarbon-rich Neuquen Province. It also comes on the heels of recent joint exploration efforts by Americas Petrogas and Apache Corp. (APA) in the area.

According to recent U.S. Energy Information Administration report, Argentina ranks No. 3 in the world in terms of technically recoverable shale-gas resources with 774 trillion cubic feet of gas.

"We believe the next major shale development outside of North America will be in the Neuquen Basin," Daniel De Nigris, Exxon's general manager for Argentine exploration, said in the statement.

Americas Petrogas and Exxon will focus their exploration activities in the Los Toldos blocks, a 660-square-kilometer (264-square-mile) area in the western region of the Neuquen Basin.

Americas Petrogas is the operator of the blocks and expects to drill the first well in the fourth quarter of 2011.

The blocks are "in a favorable location relative to other recent discoveries of shale oil and shale gas in the Vaca Muerta formation," Americas Petrogas said in a statement.

The Vaca Muerta shale formation spreads across some 21,250 square kilometers, or around 8,500 square miles. Its depth varies between 5,500 and 14,000 feet and is up to 2,000 feet thick in some areas.

"The Vaca Muerta characteristics are believed to be similar to shale reservoirs such as the Eagle Ford, Haynesville and Horn River in North America which have so far resulted in discoveries of both shale gas and shale oil," the statement said.

Other companies, including Argentine oil and gas firm YPF SA (YPF.BA, YPFD), are also exploring in the region. In July, YPF said it made a shale-oil discovery in Neuquen that will add between 10 million and 50 million barrels of crude oil to its resources in Vaca Muerta.

YPF said last December it had found an estimated 4.5 trillion cubic feet of unconventional gas in that area. YPF has earmarked $270 million for Neuquen exploration this year, and $200 million for 2012.

-By Taos Turner, Dow Jones Newswires; 5411-4103-6728;

taos.turner@dowjones.com