This week, the overall grades of 11 oil and gas stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Rhino Resource Partners LP (RNO) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Rhino Resource Partners produces, processes and sells high quality coal of various steam and metallurgical grades. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Revisions and Sales Growth, RNO also gets an F. To get an in-depth look at RNO, get Portfolio Grader’s complete analysis of RNO stock.

This week, PDC Energy (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. The stock gets F’s in Earnings Revisions and Cash Flow. As of Jan. 3, 2014, 12.3% of outstanding PDC Energy shares were held short. For more information, get Portfolio Grader’s complete analysis of PETD stock.

The rating of Petrobras Argentina SA Sponsored ADR Class B (PZE) slips from a C to a D. Petrobras Energia explores for, produces, refines, and transports oil and natural gas in South America. The stock gets F’s in Earnings Momentum and Sales Growth. For a full analysis of PZE stock, visit Portfolio Grader.

Warren Resources, Inc.’s (WRES) rating weakens this week, dropping to a D versus last week’s C. Warren Resources is an independent energy company engaged in the exploration and development of domestic onshore oil and gas reserves. For more information, get Portfolio Grader’s complete analysis of WRES stock.

This is a rough week for Uranium Energy (UEC). The company’s rating falls to F from the previous week’s D. Uranium Energy is an exploration-stage company that explores and develops mineral properties in the United States and Paraguay. The stock gets F’s in Earnings Revisions, Equity, Cash Flow and Sales Growth. As of Jan. 3, 2014, 15.3% of outstanding Uranium Energy shares were held short. For a full analysis of UEC stock, visit Portfolio Grader.

Triangle Petroleum Corporation. (TPLM) earns a D this week, falling from last week’s grade of C. Triangle Petroleum acquires, explores, and develops mineral properties. The stock gets F’s in Earnings Revisions, Earnings Surprise and Cash Flow. The stock currently has a trailing PE Ratio of 42.60. To get an in-depth look at TPLM, get Portfolio Grader’s complete analysis of TPLM stock.

Anadarko Petroleum Corporation (APC) earns an F this week, moving down from last week’s grade of D. Anadarko Petroleum engages in the exploration, development, production, and marketing of natural gas, crude oil, condensate, and natural gas liquids (NGLs) in the United States and internationally. For more information, get Portfolio Grader’s complete analysis of APC stock.

Slipping from a C to a D rating, Sasol Limited Sponsored ADR (SSL) takes a hit this week. Sasol is an integrated energy and chemicals company with production facilities in South Africa, Europe, North America and Asia. The stock also gets an F in Sales Growth. The trailing PE Ratio for the stock is 107.50. For a full analysis of SSL stock, visit Portfolio Grader.

This week, TransGlobe Energy Corporation (TGA) drops from a D to an F rating. TransGlobe Energy is mainly engaged in the exploration for, and the development and production of, oil and gas in Egypt and Yemen. The stock also gets an F in Earnings Surprise. As of Jan. 3, 2014, 23.3% of outstanding TransGlobe Energy Corporation shares were held short. To get an in-depth look at TGA, get Portfolio Grader’s complete analysis of TGA stock.

The rating of SandRidge Energy, Inc. (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 Momentum, Equity and Cash Flow. Margin Growth and Sales Growth also get F’s. As of Jan. 3, 2014, 12.6% of outstanding SandRidge Energy, Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of SD stock.

Gevo (GEVO) gets weaker ratings this week as last week’s D drops 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 Jan. 3, 2014, 11.2% of outstanding Gevo shares were held short. For a full analysis of GEVO 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.