The ratings of 20 Oil and Gas stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Pioneer Southwest Energy Partners (NYSE:PSE) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Pioneer Southwest Energy Partners seeks to own and acquire developed oil and gas properties. In Portfolio Grader’s specific subcategories of Earnings Momentum and Earnings Surprise, PSE also gets F’s. For a full analysis of PSE stock, visit Portfolio Grader.

Encana (NYSE:ECA) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Encana Corporation provides energy transportation, distribution, and related services in North America and internationally. The stock gets F’s in Earnings Growth, Earnings Momentum, and Equity. Cash Flow, Margin Growth, and Sales Growth also get F’s. To get an in-depth look at ECA, get Portfolio Grader’s complete analysis of ECA stock.

Consol Energy‘s (NYSE:CNX) rating weakens this week, dropping to an F versus last week’s D. Consol Energy is an energy producer and energy services provider that mainly serves the electric power generation industry in the United States. The stock also gets an F in Sales Growth. For a full analysis of CNX stock, visit Portfolio Grader.

This week, Gevo‘s (NASDAQ:GEVO) rating worsens to an F from the company’s D rating a week ago. Gevo operates as a technology development company for biobutanol. The stock gets F’s in Equity, Cash Flow, and Sales Growth. The stock price has dropped 17.6% over the past month, worse than the 5.7% increase the Nasdaq has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of GEVO stock.

The rating of Martin Midstream Partners (NASDAQ:MMLP) declines this week from a C to a D. Martin Midstream Partners provides marine transportation, terminalling, distribution and logistical services for producers and suppliers of hydrocarbon products, specialty chemicals and other liquids. The stock gets F’s in Earnings Revisions, Earnings Surprise, and Cash Flow. The stock’s trailing PE Ratio is 36.9. Shares of the company have dropped 5.1% over the past month. To get an in-depth look at MMLP, get Portfolio Grader’s complete analysis of MMLP stock.

This week, Penn Virginia (NYSE:PVA) drops from a C to a D rating. Penn Virginia explores for and produces oil and natural gas. The stock gets F’s in Equity and Cash Flow. Shares of PVA have gone down 2.6% from a month ago. For more information, get Portfolio Grader’s complete analysis of PVA stock.

This is a rough week for PDC Energy (NASDAQ:PETD). The company’s rating falls to D from the previous week’s C. PDC is an oil and gas company with drilling and production operations in the Rocky Mountains, the Appalachian Basin, and Michigan. The stock gets F’s in Earnings Revisions and Cash Flow. As of Aug. 24, 18.3% of outstanding PDC Energy shares were held short. For a full analysis of PETD stock, visit Portfolio Grader.

Clean Energy Fuels (NASDAQ:CLNE) earns a D this week, moving down from last week’s grade of C. Clean Energy Fuels sells natural gas fueling solutions to its customers mainly in the United States and Canada. The stock gets F’s in Equity and Cash Flow. As of Aug. 24, 20.2% of outstanding Clean Energy Fuels shares were held short. CLNE shares are down 2.5% from last month. For more information, get Portfolio Grader’s complete analysis of CLNE stock.

Concho Resources (NYSE:CXO) earns a D this week, falling from last week’s grade of C. Concho Resources engages in the acquisition, exploration, and development of oil and natural gas properties in the United States. The stock gets F’s in Earnings Momentum and Earnings Surprise. For a full analysis of CXO stock, visit Portfolio Grader.

The rating of Copano Energy (NASDAQ:CPNO) declines this week from a C to a D. Copano Energy provides midstream services to natural gas producers in the United States. The stock receives F’s in Equity, Cash Flow, Margin Growth, and Sales Growth. To get an in-depth look at CPNO, get Portfolio Grader’s complete analysis of CPNO stock.

Abraxas (NASDAQ:AXAS) earns an F this week, moving down from last week’s grade of D. Abraxas Petroleum is an independent energy company that engages in the acquisition, development, exploration, and production of oil and gas in the United States and Canada. The stock gets F’s in Earnings Revisions, Earnings Surprise, and Cash Flow. Share prices fell 24.2% over the past month. As of Aug. 24, 12.4% of outstanding Abraxas shares were held short. For more information, get Portfolio Grader’s complete analysis of AXAS stock.

This week, NuSTAR GP Holdings‘s (NYSE:NSH) rating worsens to a D from the company’s C rating a week ago. Nustar operates oil pipelines, terminals, and storage facilities. The stock gets F’s in Earnings Growth, Earnings Momentum, Earnings Revisions, and Sales Growth. The trailing PE Ratio for the stock is 87.4. For a full analysis of NSH stock, visit Portfolio Grader.

Slipping from a C to a D rating, North European Oil Royalty Trust (NYSE:NRT) takes a hit this week. North European Oil Royalty Trust is involved in gas and oil production. It holds overriding royalty rights in certain concessions or leases in the Federal Republic of Germany. The stock also rates an F in Sales Growth. Wall Street appears to agree with the stock downgrade, with share prices dropping 3.4% over the past month. To get an in-depth look at NRT, get Portfolio Grader’s complete analysis of NRT stock.

Statoil (NYSE:STO) experiences a ratings drop this week, going from last week’s C to a D. StatoilHydro ASA is involved in the development, production, transportation and marketing of crude oil, natural gas and extract natural gas liquids. For more information, get Portfolio Grader’s complete analysis of STO stock.

Petrobras Petroleo Brasileiro (NYSE:PBR) is having a tough week. The company’s rating falls from a D to an F rating. Petroleo Brasileiro S.A. explores for and produces oil and natural gas. The stock also gets an F in Cash Flow. To get an in-depth look at PBR, get Portfolio Grader’s complete analysis of PBR stock.

ECA Marcellus Trust (NYSE:ECT) earns a D this week, falling from last week’s grade of C. ECA Marcellus Trust holds royalty interests in producing and development horizontal natural gas wells for Energy Corporation of America (ECA). Investors seem to agree with the downgrade and have pushed down the share price 3.8% over the past month. For a full analysis of ECT stock, visit Portfolio Grader.

Kosmos Energy (NYSE:KOS) gets weaker ratings this week as last week’s D drops to an F. Kosmos Energy is an oil and gas exploration and production company. The stock gets F’s in Earnings Momentum, Earnings Revisions, and Sales Growth. KOS shares are down 6.8% from a month ago. To get an in-depth look at KOS, get Portfolio Grader’s complete analysis of KOS stock.

This week, Hugoton Royalty Trust (NYSE:HGT) drops from a D to an F rating. Hugoton Royalty Trust owns net profit interests in natural gas producing properties located in the Hugoton area of Kansas and Oklahoma, the Anadarko Basin of Oklahoma, and the Green River Basin of Wyoming. The stock gets F’s in Earnings Growth and Sales Growth. The stock price has fallen 13.2% over the past month. For a full analysis of HGT stock, visit Portfolio Grader.

The rating of Scorpio Tankers (NYSE:STNG) slips from a C to a D. Scorpio Tankers provides seaborne transportation of crude oil and other petroleum products worldwide. The stock gets F’s in Earnings Momentum, Equity, and Cash Flow. Investors seem to agree with the downgrade and have pushed down the share price 1.1% over the past month. For more information, get Portfolio Grader’s complete analysis of STNG stock.

This is a rough week for Frontline (NYSE:FRO). The company’s rating falls to F from the previous week’s D. Frontline owns a fleet of very large crude carriers and Suezmax tankers that transport crude oil and oil products between ports. The stock gets F’s in Earnings Momentum, Equity, and Cash Flow. Margin Growth and Sales Growth also get F’s. Wall Street appears to agree with the stock downgrade, with share prices dropping 1.9% over the past month. As of Aug. 24, 13.1% of outstanding Frontline shares were held short. For a full analysis of FRO stock, visit Portfolio Grader.

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.