This week, three Oil and Gas stocks are improving their overall ratings on Portfolio Grader. Each of these stocks is rated an “A” (“strong buy”) or “B” overall (“buy”).

Chesapeake Midstream Partners’ (NYSE:CHKM) grade is moving up to a B (“buy”) this week from last week’s C (“hold”). Chesapeake Midstream Partners owns, operates, develops, and acquires natural gas, natural gas liquids, and oil gathering systems, as well as other midstream energy assets in the United States. For more information, get Portfolio Grader’s complete analysis of CHKM stock.

Oiltanking Partners, L.P. (NYSE:OILT) is making headway this week, with the company’s rating improving to an A (“strong buy”) from a B (“buy”) last week. Oiltanking Partners engages in the terminaling, storage and transportation of crude oil, refined petroleum products and liquefied petroleum gas. Shares of OILT have increased 10.9% over the past month, better than the 1.7% decrease the S&P 500 has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of OILT stock.

Cabot Oil & Gas Corporation (NYSE:COG) gets a higher grade this week, advancing from a B last week to an A. Cabot Oil & Gas is an independent company that develops, explores, produces and markets natural gas, and transports, stores, and gathers it for resale. For more information, get Portfolio Grader’s complete analysis of COG stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.