U.S. midstream energy partnership Summit Midstream Partners L.P. (SMLP) plans to issue $300 million in senior unsecured notes due 2021 through its wholly owned subsidiary Summit Midstream Holdings LLC. Holdings intends to use net proceeds to repay outstanding debt under its revolving credit facility associated with its recent acquisitions of Bison Midstream LLC from its parent, Summit Midstream Partners Holdings LLC and Sherwood Gathering and Compression System from MarkWest Energy Partners L.P. (renamed Mountaineer Midstream Company LLC). We are assigning our 'B+' corporate credit rating to SMLP. In addition, we are assigning a 'B' issue-level rating to the notes. The stable outlook on SMLP reflects our expectation that it will maintain adjusted debt to EBITDA of about 4x in 2013