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 Nov. 1, 2013, 17% of outstanding PDC Energy shares were held short. For more information, get Portfolio Grader’s complete analysis of PETD stock.

This is a rough week for EOG Resources, Inc. (NYSE:EOG). The company’s rating falls to D from the previous 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 trailing PE Ratio for the stock is 76.60. To get an in-depth look at EOG, get Portfolio Grader’s complete analysis of EOG stock.

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. The stock’s trailing PE Ratio is 46.50. For a full analysis of SU stock, visit Portfolio Grader.

Enbridge Energy Partners, L.P. Class A’s (NYSE:EEP) rating weakens this week, dropping to an F versus last 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 receives F’s in Earnings Growth, Earnings Revisions, and Earnings Surprise. Cash Flow and Sales Growth also get F’s. The stock currently has a trailing PE Ratio of 77.40. For more information, get Portfolio Grader’s complete analysis of EEP stock.

PVR Partners, L.P. (NYSE:PVR) gets weaker ratings this week as last week’s C drops 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 rates an F in Earnings Growth, Earnings Revisions, and Equity. Cash Flow, Margin Growth, and Sales Growth also get F’s. The stock has a trailing PE Ratio of 107.50. To get an in-depth look at PVR, get Portfolio Grader’s complete analysis of PVR stock.

This week, Green Plains Renewable Energy, Inc. (NASDAQ:GPRE) drops from a C to a D rating. 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. 1, 2013, 16.1% of outstanding Green Plains Renewable Energy, Inc. shares were held short. For a full analysis of GPRE stock, visit Portfolio Grader.

Slipping from a C to a D rating, Chevron Corporation (NYSE:CVX) takes a hit this week. 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.

ONEOK Partners, L.P. (NYSE:OKS) is having a tough week. The company’s rating falls from a C to a D. 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. For a full analysis of OKS stock, visit Portfolio Grader.

Continental Resources, Inc. (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’s trailing PE Ratio is 31.70. For more information, get Portfolio Grader’s complete analysis of CLR stock.

Teekay Corporation (NYSE:TK) earns a D this week, falling from last week’s grade of C. 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. For a full analysis of TK stock, visit Portfolio Grader.

The rating of Frontline (NYSE:FRO) slips 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. The stock price has fallen 20.6% 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. 1, 2013, 13.1% of outstanding Frontline shares were held short. For more information, get Portfolio Grader’s complete analysis of FRO stock.

Endeavour International Corporation (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. As of Nov. 1, 2013, 19.2% of outstanding Endeavour International Corporation shares were held short. To get an in-depth look at END, get Portfolio Grader’s complete analysis of END stock.

This week, North European Oil Royalty Trust’s (NYSE:NRT) rating worsens to an F from the company’s D rating a week ago. 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.

The rating of SandRidge Energy, Inc. (NYSE:SD) declines this week from a D to an F. 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. To get an in-depth look at SD, get Portfolio Grader’s complete analysis of SD stock.

Gevo (NASDAQ:GEVO) experiences a ratings drop this week, going from last week’s D to an F. Gevo operates as a technology development company for biobutanol. The stock gets F’s in Equity, Cash Flow, and Sales Growth. As of Nov. 1, 2013, 16.7% of outstanding Gevo shares were held short. For more information, get Portfolio Grader’s complete analysis of GEVO stock.

Teekay Offshore Partners L.P. (NYSE:TOO) earns a D this week, falling from last week’s grade of C. 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.