The overall ratings of 16 Oil and Gas stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, PDC Energy (NASDAQ:PETD) falls to a D (“sell”), worse than last week’s grade of C (“hold”). PDC is an oil and gas company with drilling and production operations in the Rocky Mountains, the Appalachian Basin, and Michigan. In Portfolio Grader’s specific subcategories of Earnings Revisions and Cash Flow, PETD also gets F’s. As of April 5, 2013, 21% of outstanding PDC Energy shares were held short. For more information, get Portfolio Grader’s complete analysis of PETD stock.

This week, EOG Resources’ (NYSE:EOG) rating worsens to a D from the company’s C rating a week ago. EOG Resources is in the business of the exploration, development, production, and marketing of natural gas and crude oil. The stock gets F’s in Earnings Growth, Earnings Momentum, and Margin Growth. The trailing PE Ratio for the stock is 61.20. For a full analysis of EOG stock, visit Portfolio Grader.

Suncor Energy (NYSE:SU) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). Suncor Energy is an integrated energy company in Canada. The stock gets F’s in Earnings Momentum and Earnings Surprise. For more information, get Portfolio Grader’s complete analysis of SU stock.

Enbridge Energy Partners (NYSE:EEP) experiences a ratings drop this week, going from last week’s D to an F. Enbridge Energy Partners transports crude oil and natural gas liquids to refineries in the midwestern United States and eastern Canada. The stock receives F’s in Earnings Growth, Earnings Revisions, and Earnings Surprise. Cash Flow and Sales Growth also get F’s. To get an in-depth look at EEP, get Portfolio Grader’s complete analysis of EEP stock.

This is a rough week for PVR Partners L.P. (NYSE:PVR). The company’s rating falls to D from the previous week’s C. Penn Virginia Resource Partners owns and operates a network of natural gas pipelines and processing plants which provide gathering, transportation, compression, processing, dehydration and related services to natural gas producers. For more information, get Portfolio Grader’s complete analysis of PVR stock.

Slipping from C to a D rating, Green Plains Renewable Energy (NASDAQ:GPRE) takes a hit this week. Green Plains Renewable Energy, Inc. was formed in June 2004 to construct and operate dry mill, fuel-grade ethanol production facilities. Ethanol is a renewable, environmentally clean fuel source that is produced at numerous facilities in the United States, mostly in the Midwest. The stock gets F’s in Earnings Growth, Earnings Revisions, and Margin Growth. The stock currently has a trailing PE Ratio of 27.50. For a full analysis of GPRE stock, visit Portfolio Grader.

Chevron (NYSE:CVX) is having a tough week. The company’s rating falls from C to a D. Chevron gives management and technological support to international subsidiaries that operate petroleum, chemicals, mining, power generation, and energy services. The stock also gets an F in Sales Growth. To get an in-depth look at CVX, get Portfolio Grader’s complete analysis of CVX stock.

The rating of ONEOK Partners (NYSE:OKS) declines this week from C to a D. ONEOK Partners, L. P. is a publicly traded Delaware master limited partnership that was formed in 1993. The stock also rates an F in Sales Growth. For more information, get Portfolio Grader’s complete analysis of OKS stock.

Continental Resources (NYSE:CLR) earns an F this week, moving down from last week’s grade of D. Continental Resources explores for, develops, and produces oil and natural gas properties in the United States. In Earnings Growth, Earnings Momentum, Cash Flow, and Sales Growth the stock gets F’s. The stock price has fallen 9.6% over the past month, worse than the 1.2% increase the S&P 500 has seen over the same period of time. For a full analysis of CLR stock, visit Portfolio Grader.

The rating of Teekay Corp. (NYSE:TK) slips from C to a D. Teekay is a provider of international crude oil and petroleum product transportation services. The stock gets F’s in Earnings Momentum, Earnings Revisions, and Earnings Surprise. Equity and Cash Flow also get F’s. To get an in-depth look at TK, get Portfolio Grader’s complete analysis of TK stock.

The rating of Frontline (NYSE:FRO) declines this week from a D to an F. Frontline owns a fleet of very large crude carriers and Suezmax tankers that transport crude oil and oil products between ports. The stock receives F’s in Earnings Revisions, Equity, Cash Flow, and Sales Growth. As of April 5, 2013, 13.5% of outstanding Frontline shares were held short. For a full analysis of FRO stock, visit Portfolio Grader.

Endeavour International (NYSE:END) experiences a ratings drop this week, going from last week’s D to an F. Endeavour International is an international oil and gas exploration and production company that acquires, explores, and develops energy reserves. The stock gets F’s in Equity and Cash Flow. Share prices fell 22.7% over the past month. As of April 5, 2013, 18.9% of outstanding Endeavour International shares were held short. For more information, get Portfolio Grader’s complete analysis of END stock.

North European Oil Royalty Trust (NYSE:NRT) gets weaker ratings this week as last week’s D drops to an F. 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 gets an F in Sales Growth. To get an in-depth look at NRT, get Portfolio Grader’s complete analysis of NRT stock.

This is a rough week for SandRidge Energy (NYSE:SD). The company’s rating falls to F from the previous week’s D. SandRidge Energy explores and produces natural gas and crude oil. The stock receives F’s in Earnings Growth, Earnings Momentum, and Equity. Cash Flow and Margin Growth also get F’s. Investors seem to agree with the downgrade and have pushed down the share price 14.6% over the past month. As of April 5, 2013, 11% of outstanding SandRidge Energy shares were held short. For more information, get Portfolio Grader’s complete analysis of SD stock.

Gevo (NASDAQ:GEVO) earns an F this week, falling from last week’s grade of D. Gevo operates as a technology development company for biobutanol. The stock gets F’s in Equity, Cash Flow, and Sales Growth. As of April 5, 2013, 17.6% of outstanding Gevo shares were held short. To get an in-depth look at GEVO, get Portfolio Grader’s complete analysis of GEVO stock.

This week, Teekay Offshore Partners (NYSE:TOO) drops from C to a D rating. Teekay Offshore Partners LP provides marine transportation and storage services to the offshore oil industry. The stock also gets an F in Sales Growth. The stock’s trailing PE Ratio is 46.00. For a full analysis of TOO 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.