The Mississippian-aged Pekisko Formation is composed predominately of platform and ramp carbonates. Its typically low porosity is enhanced along its eastern subcrop margin as a result of karst processes. Trapping occurs most often in closed structures, including outlying erosional remnants created through post-Mississippian / pre-Cretaceous erosion. Pekisko resource play drilling has been concentrated in the Princess and Judy Creek areas of southern and central Alberta. The first discovery of Pekisko oil at Princess goes back to the mid-1940s. Since that time, the Pekisko there has produced 906 E3M3 (5.7 million bbls) of oil and 414 E6M3 (14.6 bcf) of gas. Over 220 prospective sections in the Princess area have been estimated to contain between 1,272 E3M3 and 3,180 E3M3 (8 and 20 million barrels) of oil-in-place per section. Judy Creek was initially developed as a Swan Hills play in the 1950s. Targeting the Pekisko there began in the late 1980s. EUR per well at Princess ranges from 56,000 boe to 148,000 boe (depending on method used) and from 38,000 boe to 61,000 boe at Judy Creek. While still preliminary due to lack of production history in the two areas, the two ranges again highlight the difference in reservoir quality.