...+ Canada-based oil and natural gas exploration and production company GranTierra Energy Inc. is planning to issue $300 million in senior unsecured notes. + We are assigning our 'B+' long-term corporate credit rating and our issue-level rating on the company and on its proposed $300 million senior unsecured notes due 2025. + The stable outlook reflects our view that the company will likely increase oil production and reserves due to its recently acquired fields. It also reflects our expectation that the company's leverage will remain below 2x and that it will maintain its strong liquidity in the next 12-18 months. MEXICO CITY (S&P Global Ratings) Feb. 1, 2018--S&P Global Ratings assigned its 'B+' long-term corporate credit ratingto GranTierra Energy Ltd. The outlook is stable. At the same time, we assigned our 'B+' issue-level rating on the proposed $300 million senior unsecured notes due 2025, to be issued by Gran Tierra Energy International Holdings Ltd (GTEIH). The ratings on GranTierra...