 Shares of Chesapeake Energy Corp. CHK, 0.58 edged up 0.1 in morning trading Monday, after SP Global Ratings raised its rating on the oil and gas exploration companys credit, citing a favorable operational and financial track record since merging from bankruptcy early last year. The rating moved up one notch to BB from BB-, but the new rating remained two notches deep into speculative grade, or junk, territory. 