This week, five 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”).

Valero Energy (NYSE:VLO) is making progress this week as its rating of C (“hold”) from last week increases to a B (“buy”) rating this week. Valero is an independent petroleum refiner and marketer. In Portfolio Grader’s specific subcategory of Earnings Revisions, VLO also gets an A. Shares of VLO have increased 8% over the past month, better than the 3% increase the S&P 500 has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of VLO stock.

HollyFrontier (NYSE:HFC) earns a B this week, jumping up from last week’s grade of C. Holly refines, transports, stores and markets petroleum products. The stock has a trailing PE Ratio of 5.9. For more information, get Portfolio Grader’s complete analysis of HFC stock.

This week, Sunoco (NYSE:SUN) is making solid headway. The company’s rating improves to an A (“strong buy”) from last week’s B (“buy”) rating. Sunoco is a petroleum refiner and marketer, as well as a manufacturer of chemicals. For more information, get Portfolio Grader’s complete analysis of SUN stock.

This is a strong week for Chesapeake Midstream Partners (NYSE:CHKM). The company’s rating climbs to B from the previous week’s C. 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.

The rating of Regency Energy Partners (NYSE:RGP) moves up this week, rising from a C to a B. Regency Energy Partners is an independent midstream energy partnership involved in the gathering, processing, marketing, and transportation of natural gas and natural gas liquids. For more information, get Portfolio Grader’s complete analysis of RGP 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.