The new report of the U.S. Energy Information Agency provides an initial assessment of shale oil resources and updates a prior assessment of shale gas resources issued in April 2011. It assesses 137 shale formations in 41 countries outside the United States, expanding on the 69 shale formations within 32 countries considered in the prior report. It is the most comprehensive global resource estimate. Read the executive summary here (in English only).

The report states that the worldwide shale gas resources add approximately 47 percent to the 15,583 trillion cubic feet of proved and unproven nonshale technically recoverable natural gas resources. The estimates of technically recoverable shale gas resources are presented also in country-level detail. 

Table 1 below presents the 5 countries with the highest estimate for shale gas resources and the EIA 2013 estimates for European countries. Additionaly it includes the estimates from the EIA 2011 report and adds two other resource estimates, recently published for Poland and Germany by the countries´ national geological surveys. 

The changes in EIA estimates from different years as well as the differences between EIA estimates and estimates from other sources highlights the volatitily in shale gas resource estimates. This is, among others, due to a lack of accepted common calculation methods and a steadily growing body of data. However, reliable shale gas resource estimates will be available only after exploratory drilling, which has been done in a few countries worldwide only. 

Tab 1: Shale gas resource estimates from U.S. EIA (published in 2011 and 2013) and other sources. * Estimate from the Polish PGI-NRI (March 2012); ** Estimate from the German BGR (May 2012)