The overall ratings of 18 oil and gas stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Phillips 66 (PSX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Phillips 66 is an advantaged downstream energy company. It operates through the following businesses segments: Refining and Marketing, Midstream and Chemicals. The Refining and Marketing segment purchases, refines, markets and transports crude oil and petroleum products in the United States, Europe … In Portfolio Grader’s specific subcategories of Earnings Growth and Earnings Revisions, PSX also gets F’s. For a full analysis of PSX stock, visit Portfolio Grader.

This week, PDC Energy’s (PETD) rating worsens to a D from the company’s C rating a week ago. 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 Dec. 6, 2013, 12.5% 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.

This is a rough week for EOG Resources, Inc. (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 stock currently has a trailing PE Ratio of 40.90. For a full analysis of EOG stock, visit Portfolio Grader.

Suncor Energy (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. To get an in-depth look at SU, get Portfolio Grader’s complete analysis of SU stock.

Enbridge Energy Partners, L.P. Class A (EEP) earns an F this week, moving down from last week’s grade of 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 49.30. For more information, get Portfolio Grader’s complete analysis of EEP stock.

The rating of PVR Partners, L.P. (PVR) slips from a C to a D. Penn Virginia Resource 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 rates an F in Earnings Growth, Earnings Revisions and Equity. Cash Flow, Margin Growth and Sales Growth also get F’s. The stock currently has a trailing PE Ratio of 80.70. For a full analysis of PVR stock, visit Portfolio Grader.

Green Plains Renewable Energy, Inc. (GPRE) is having a tough week. The company’s rating falls 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 Dec. 6, 2013, 16.7% of outstanding Green Plains Renewable Energy, Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of GPRE stock.

This week, Chevron Corporation (CVX) drops from a C to a D rating. 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.

Slipping from a C to a D rating, ONEOK Partners, L.P. (OKS) takes a hit this week. ONEOK Partners is engaged in the gathering, processing, storage, and transportation of natural gas in the United States. The stock also gets an F in Sales Growth. For a full analysis of OKS stock, visit Portfolio Grader.

The rating of Continental Resources, Inc. (CLR) declines this week from a D to an F. Continental Resources explores for, develops, and produces oil and natural gas properties in the United States. The stock gets F’s in Earnings Growth, Earnings Momentum, Cash Flow and Sales Growth. To get an in-depth look at CLR, get Portfolio Grader’s complete analysis of CLR stock.

Teekay Corporation (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. For more information, get Portfolio Grader’s complete analysis of TK stock.

This week, Frontline’s (FRO) rating worsens to an F from the company’s D rating a week ago. Frontline owns a fleet of very large crude carriers and Suezmax tankers that transport crude oil and oil products between ports. In Earnings Revisions, Equity, Cash Flow and Sales Growth the stock gets F’s. As of Dec. 6, 2013, 12.8% of outstanding Frontline shares were held short. To get an in-depth look at FRO, get Portfolio Grader’s complete analysis of FRO stock.

Endeavour International Corporation (END) earns an F this week, falling from last week’s grade of D. 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 Dec. 6, 2013, 20.2% of outstanding Endeavour International Corporation shares were held short. For a full analysis of END stock, visit Portfolio Grader.

North European Oil Royalty Trust (NRT) earns an F this week, moving down from last week’s grade of D. North European Oil Royalty Trust is involved in gas and oil production, and 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. For more information, get Portfolio Grader’s complete analysis of NRT stock.

This week, SandRidge Energy, Inc. (SD) drops from a D to an F rating. 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. As of Dec. 6, 2013, 12.8% of outstanding SandRidge Energy, Inc. shares were held short. To get an in-depth look at SD, get Portfolio Grader’s complete analysis of SD stock.

The rating of Gevo (GEVO) slips from a 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 Dec. 6, 2013, 17.1% of outstanding Gevo shares were held short. For more information, get Portfolio Grader’s complete analysis of GEVO stock.

Teekay Offshore Partners L.P. (TOO) gets weaker ratings this week as last week’s C drops to a D. Teekay Offshore Partners LP provides marine transportation and storage services to the offshore oil industry. The stock also gets an F in Sales Growth. For a full analysis of TOO stock, visit Portfolio Grader.

Linn Co. LLC’s (LNCO) rating weakens this week, dropping to a D versus last week’s C. Linn Co. LLC operates as a development stage company. The company created to enhance Linn Energy LLC’s (LINN) ability to raise additional equity capital to execute on its acquisition and growth strategy. It’s sole purpose is to own LINN units and has no assets or operations other than those related … The stock has a trailing PE Ratio of 74.40. For more information, get Portfolio Grader’s complete analysis of LNCO 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.