A little-known shale oil play in Oklahoma is attracting more drilling and investment as rising output from newer wells is enticing companies to boost production beyond the giant Permian basin in Texas. The Meramec formation is a part of what is called the STACK region - Sooner Trend Anadarko basin Canadian and Kingfisher counties - where companies such as Marathon Oil and Devon Energy bought up acreage following the oil slump in 2014. Those investments are now paying off as production levels rise and soaring land costs in the Permian have producers looking to other fields for expansion. Leading the pack is Oklahoma-based Devon Energy Corp, which expects its STACK production to reach 140,000 barrels of oil equivalent per day (boed) by the end of 2018, up from 107,000 boed a year ago. Devon, also a Permian operator, said in a presentation earlier this month that it has earmarked more than 95 percent of its STACK budget for Meramec although it did not disclose dollar values.