From Bloomberg News on Thursday:

By Joe Carroll

Exxon Mobil Corp. increased the proportion of its reserves made up of oil to the highest in a decade as shale-drilling expertise acquired in the $35 billion XTO Energy deal was mobilized to find crude.

The world’s largest energy explorer by market value boosted the liquid hydrocarbons component of its global reserves to 53 percent last year from 51 percent in 2012, Exxon said in a statement today. It was the third consecutive annual increase in the so-called oil cut for the Irving, Texas-based crude and natural gas producer, according to data compiled by Bloomberg.

Exxon’s June 2010 acquisition of shale-gas explorer XTO has been criticized by analysts including Brian Youngberg of Edward Jones & Co. and Paul Sankey, formerly of Deutsche Bank AG who starts at Wolfe Research LLC March 17, as an ill-timed bet on North American gas. Critics said the purchase would bloat Exxon with additional gas reserves at a time when a glut of domestic supply from shale fields was collapsing the profitability of pumping the fuel.

In the 22 months after the XTO transaction closed, U.S. gas prices tumbled 59 percent to the lowest in a decade, prompting the deal’s architect, Exxon Chairman and Chief Executive Officer Rex Tillerson, to publicly bemoan that gas producers were “all losing our shirts.”Shale Fields

Exxon finished 2013 with proved reserves equivalent to 25.2 billion barrels of oil, 47 percent of which were comprised of gas, according to today’s statement. The company discovered and acquired enough new crude and gas to replace 103 percent of what it pumped last year.

The company cited the Upper Zakum oilfield in Abu Dhabi as a major source of new liquid reserves, as well as North American shale formations such as the Permian and Bakken. Exxon has been deploying XTO’s fracturing experts to shale fields to speed the development of resources.

The 53 percent liquids portion of total reserves was the highest since 2003, when it reached 57 percent, according to data compiled by Bloomberg.

Exxon fell 0.4 percent to $95.03 at the close in New York. The stock has risen 7.3 percent in the past year.