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”).

PDC Energy (NASDAQ:PETD) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. 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 Nov. 8, 2013, 14.5% of outstanding PDC Energy shares were held short. To get an in-depth look at PETD, get Portfolio Grader’s complete analysis of PETD stock.

EOG Resources, Inc.’s (NYSE:EOG) rating weakens this week, dropping to a D versus last week’s C. 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 stock’s trailing PE Ratio is 48.80. For a full analysis of EOG stock, visit Portfolio Grader.

Suncor Energy (NYSE:SU) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a 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.

This is a rough week for Enbridge Energy Partners, L.P. Class A (NYSE:EEP). The company’s rating falls to F from the previous week’s D. Enbridge Energy Partners transports crude oil and natural gas liquids to refineries in the midwestern United States and eastern Canada. The stock gets F’s in Earnings Growth, Earnings Revisions, and Earnings Surprise. Cash Flow and Sales Growth also get F’s. The trailing PE Ratio for the stock is 50.50. For a full analysis of EEP stock, visit Portfolio Grader.

The rating of PVR Partners, L.P. (NYSE:PVR) declines this week from a C to a D. 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. The stock has a trailing PE Ratio of 102.60. For more information, get Portfolio Grader’s complete analysis of PVR stock.

The rating of Green Plains Renewable Energy, Inc. (NASDAQ:GPRE) slips from a C to a D. Green Plains Renewable Energy constructs and operates dry mill, fuel-grade ethanol production facilities. The stock gets F’s in Earnings Growth, Earnings Revisions, and Margin Growth. As of Nov. 8, 2013, 15.9% of outstanding Green Plains Renewable Energy, Inc. shares were held short. To get an in-depth look at GPRE, get Portfolio Grader’s complete analysis of GPRE stock.

This week, Chevron Corporation’s (NYSE:CVX) rating worsens to a D from the company’s C rating a week ago. 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. For a full analysis of CVX stock, visit Portfolio Grader.

ONEOK Partners, L.P. (NYSE:OKS) earns a D this week, moving down from last week’s grade of C. ONEOK Partners is engaged in the gathering, processing, storage, and transportation of natural gas in the United States. The stock also rates an F in Sales Growth. To get an in-depth look at OKS, get Portfolio Grader’s complete analysis of OKS stock.

Continental Resources, Inc. (NYSE:CLR) earns an F this week, falling 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 trailing PE Ratio for the stock is 30.10. For more information, get Portfolio Grader’s complete analysis of CLR stock.

Teekay Corporation (NYSE:TK) gets weaker ratings this week as last week’s C drops to a D. Teekay is a provider of international crude oil and petroleum product transportation services. The stock receives 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.

This week, Frontline (NYSE:FRO) drops from a D to an F rating. 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 Revisions, Equity, Cash Flow, and Sales Growth. As of Nov. 8, 2013, 13.1% of outstanding Frontline shares were held short. For a full analysis of FRO stock, visit Portfolio Grader.

Slipping from a D to an F rating, Endeavour International Corporation (NYSE:END) takes a hit this week. 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. The stock price has fallen 22.5% over the past month, worse than the 1.7% decrease the S&P 500 has seen over the same period of time. As of Nov. 8, 2013, 19.2% of outstanding Endeavour International Corporation shares were held short. For more information, get Portfolio Grader’s complete analysis of END stock.

North European Oil Royalty Trust (NYSE:NRT) experiences a ratings drop this week, going from last week’s D 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. For a full analysis of NRT stock, visit Portfolio Grader.

SandRidge Energy, Inc. (NYSE:SD) gets weaker ratings this week as last week’s D drops to an F. SandRidge Energy explores and produces natural gas and crude oil. The stock gets F’s in Earnings Growth, Earnings Momentum, and Equity. Cash Flow and Margin Growth also get F’s. For more information, get Portfolio Grader’s complete analysis of SD stock.

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. As of Nov. 8, 2013, 16.6% 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 L.P. (NYSE:TOO) drops from a C to a D rating. Teekay Offshore Partners LP provides marine transportation and storage services to the offshore oil industry. The stock also rates an F in Sales Growth. 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.