The grades of nine oil and gas stocks are better this week, according to the Portfolio Grader database. Every one of these stocks has an “A” (“strong buy”) or “B” overall (“buy”) rating.

Chesapeake Midstream Partners (CHKM) ups its rating to a B (“buy”) this week after earning a C (“hold”) in the week before. 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.

Diamondback Energy, Inc. (FANG) is progressing from last week’s rating of B (“buy”) as the company improves to an A (“strong buy”) this week. Shares of FANG have increased 5.4% over the past month, better than the 1.3% decrease the Nasdaq has seen over the same period of time. Shares of the stock have been trading at an exceptionally rapid pace, up twofold from the week prior. For more information, get Portfolio Grader’s complete analysis of FANG stock.

PVR Partners, L.P.’s (PVR) ratings are looking better this week, moving up to a B from last week’s C. PVR Partners owns and operates a network of natural gas pipelines and processing plants that provide gathering, transportation, compression, processing, dehydration and related services to natural gas producers. The stock has a dividend yield of 2.2%. For more information, get Portfolio Grader’s complete analysis of PVR stock.

This is a strong week for Carrizo Oil & Gas, Inc. (CRZO). The company’s rating climbs to A from the previous week’s B. Carrizo Oil & Gas is engaged in the exploration, development, production and transportation of natural gas and oil, mainly in the United States. At $55.68, the stock is above the 50-day moving average of $52.25. For more information, get Portfolio Grader’s complete analysis of CRZO stock.

U.S. Energy Corp. (USEG) is seeing ratings go up from a C last week to a B this week. U. S. Energy explores for oil and natural gas. For more information, get Portfolio Grader’s complete analysis of USEG stock.

Frontline (FRO) earns a B this week, jumping up from last week’s grade of C. Frontline owns a fleet of very large crude carriers and Suezmax tankers that transport crude oil and oil products between ports. Shares of the stock have been changing hands at an unusually rapid pace, twice the rate of the week prior. For more information, get Portfolio Grader’s complete analysis of FRO stock.

This week, Niska Gas Storage Partners (NKA) pushes up from a C to a B rating. Niska Gas Storage is an independent owner and operator of natural gas storage assets in North America. Shares of the stock have been trading at an exceptionally rapid pace, up 1077.5% from the week prior. For more information, get Portfolio Grader’s complete analysis of NKA stock.

The rating of Advantage Oil & Gas (AAV) moves up this week, rising from a C to a B. Advantage Oil & Gas is actively engaged in the business of oil and gas exploitation, development, acquisition and production. The stock’s price of $6.10 is above the 50-day moving average of $5.04. Shares of the stock have been trading at an exceptionally rapid pace, up twofold from the week prior. For more information, get Portfolio Grader’s complete analysis of AAV stock.

This week, Cross Timbers Royalty’s (CRT) ratings are up from a B last week to an A. Cross Timbers Royalty is an express trust in the United States. At $32.40, the stock is above the 50-day moving average of $30.72. The stock’s dividend yield is 2.5%. For more information, get Portfolio Grader’s complete analysis of CRT 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.