This week, the ratings of 16 oil and gas stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Summit Midstream Partners LP (SMLP) falls to a D (“sell”), worse than last week’s grade of C (“hold”). In Portfolio Grader’s specific subcategories of Earnings Revisions, Earnings Surprise and Margin Growth, SMLP also gets an F. The stock has a trailing PE Ratio of 75.50. For more information, get Portfolio Grader’s complete analysis of SMLP stock.

Crestwood Equity Partners LP (CEQP) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Crestwood Equity Partners operates in natural gas storage in Texas, and in natural gas, liquid and crude oil services serving customers in the United States and Canada. The stock gets F’s in Earnings Revisions, Earnings Surprise and Cash Flow. The stock currently has a trailing PE Ratio of 43.90. To get an in-depth look at CEQP, get Portfolio Grader’s complete analysis of CEQP stock.

Alon USA Energy, Inc.’s (ALJ) rating weakens this week, dropping to a D versus last week’s C. Alon USA Energy is an independent refiner and marketer of petroleum products operating mainly in the South Central, Southwestern and Western regions of the United States. The stock also gets an F in Margin Growth. As of Dec. 24, 2014, 13.7% of outstanding Alon USA Energy, Inc. shares were held short. The trailing PE Ratio for the stock is 51.00. For more information, get Portfolio Grader’s complete analysis of ALJ stock.

Slipping from a D to an F rating, Antero Resources Corporation (AR) takes a hit this week. The stock gets F’s in Earnings Revisions, Earnings Surprise, Cash Flow and Margin Growth. To get an in-depth look at AR, get Portfolio Grader’s complete analysis of AR stock.

This week, WPX Energy, Inc. Class A (WPX) drops from a D to an F rating. WPX Energy is an independent natural gas and oil exploration and production company which is engaged in the exploitation and development of long-life unconventional properties. The stock gets F’s in Earnings Revisions, Equity and Cash Flow. For more information, get Portfolio Grader’s complete analysis of WPX stock.

This week, Ship Finance International Limited’s (SFL) rating worsens to a D from the company’s C rating a week ago. Ship Finance International is engaged mainly in the ownership and operation of vessels and offshore-related assets. The stock also gets an F in Cash Flow. To get an in-depth look at SFL, get Portfolio Grader’s complete analysis of SFL stock.

The rating of CVR Energy, Inc. (CVI) declines this week from a C to a D. CVR Energy engages in refining and marketing transportation fuels in the United States. The stock gets F’s in Earnings Growth, Cash Flow and Margin Growth. For more information, get Portfolio Grader’s complete analysis of CVI stock.

Murphy Oil Corporation (MUR) earns an F this week, falling from last week’s grade of D. Murphy Oil is a worldwide oil and gas exploration and production company with refining and marketing operations in the United States and the United Kingdom. The stock gets F’s in Earnings Revisions and Cash Flow. To get an in-depth look at MUR, get Portfolio Grader’s complete analysis of MUR stock.

The rating of Amyris, Inc. (AMRS) declines this week from a C to an F. Amyris provides alternatives to a range of petroleum-sourced products used in specialty chemical and transportation fuel markets worldwide. The stock gets F’s in Earnings Revisions and Cash Flow. For more information, get Portfolio Grader’s complete analysis of AMRS stock.

Slipping from a C to a D rating, San Juan Basin Royalty Trust (SJT) takes a hit this week. San Juan Basin Royalty Trust is an express trust that holds royalty interests in properties in northwestern New Mexico. The stock also rates an F in Earnings Momentum. To get an in-depth look at SJT, get Portfolio Grader’s complete analysis of SJT stock.

Gevo’s (GEVO) rating weakens this week, dropping to an F versus last week’s D. Gevo operates as a technology development company for biobutanol. The stock gets F’s in Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of GEVO stock.

Adams Resources & Energy, Inc. (AE) is having a tough week. The company’s rating falls from a C to a D. Adams Resources & Energy engages in marketing crude oil, natural gas, and petroleum products. The stock also gets an F in Margin Growth. In the past week, trade volume fell significantly to half the previous rate. To get an in-depth look at AE, get Portfolio Grader’s complete analysis of AE stock.

This week, PDC Energy’s (PETD) rating worsens to a D from the company’s C rating a week ago. PDC Energy 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. For more information, get Portfolio Grader’s complete analysis of PETD stock.

Noble Energy, Inc. (NBL) gets weaker ratings this week as last week’s D drops to an F. Noble Energy is an independent company engaged in the acquisition, exploration, development, production and marketing of crude oil, natural gas, and natural gas liquids. In Earnings Revisions, Earnings Surprise, Cash Flow and Sales Growth the stock gets F’s. To get an in-depth look at NBL, get Portfolio Grader’s complete analysis of NBL stock.

This is a rough week for Boardwalk Pipeline Partners, LP (BWP). The company’s rating falls to D from the previous week’s C. Boardwalk Pipeline Partners engages in the ownership and operation of integrated natural gas pipelines and storage systems in the United States. The stock also gets an F in Earnings Growth. For more information, get Portfolio Grader’s complete analysis of BWP stock.

Gastar Exploration, Inc. (GST) experiences a ratings drop this week, going from last week’s D to an F. Gastar Exploration is a natural gas exploration company. The stock gets F’s in Earnings Revisions, Cash Flow and Margin Growth. To get an in-depth look at GST, get Portfolio Grader’s complete analysis of GST 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.