This report provides an initial assessment of shale oil resources and updates a prior assessment of shale gas resources iss ued 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. The earlier assessment, also prepared by Advanced Resources International (ARI), was released as part of a U.S. Energy Information Administration (EIA) report titled World Shale Gas Resources: An Initial Assessment of 14 Regions outside the United States.