For the current week, the overall ratings of 15 Oil and Gas stocks are worse, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Gevo’s (NASDAQ:GEVO) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Gevo operates as a technology development company for biobutanol. In Portfolio Grader’s specific subcategories of Equity, Cash Flow, and Sales Growth, GEVO also gets an F. As of Jan. 11, 2013, 16% of outstanding Gevo shares were held short. For a full analysis of GEVO stock, visit Portfolio Grader.

SandRidge Energy (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. As of Jan. 11, 2013, 12.7% of outstanding SandRidge Energy shares were held short. For more information, get Portfolio Grader’s complete analysis of SD stock.

Total S.A.’s (NYSE:TOT) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Total is an international oil and gas company engaged in all aspects of the petroleum industry. To get an in-depth look at TOT, get Portfolio Grader’s complete analysis of TOT stock.

Dorchester Minerals (NASDAQ:DMLP) experiences a ratings drop this week, going from last week’s C to a D. Dorchester Minerals acquires, owns, and administers producing and nonproducing natural gas and crude oil royalty, net profits, and leasehold interests in the United States. The stock also gets an F in Sales Growth. For a full analysis of DMLP stock, visit Portfolio Grader.

This week, Crosstex Energy (NASDAQ:XTEX) drops from a D to an F rating. Crosstex Energy operates as an independent midstream energy company. The stock gets F’s in Earnings Revisions, Equity, Cash Flow, and Sales Growth. For more information, get Portfolio Grader’s complete analysis of XTEX stock.

Talisman Energy (NYSE:TLM) is having a tough week. The company’s rating falls from a D to an F. Talisman Energy is a global diversified upstream oil and gas company. To get an in-depth look at TLM, get Portfolio Grader’s complete analysis of TLM stock.

Slipping from a D to an F rating, Enduro Royalty Trust (NYSE:NDRO) takes a hit this week. For more information, get Portfolio Grader’s complete analysis of NDRO stock.

Kinder Morgan Managemen (NYSE:KMR) earns a D this week, falling from last week’s grade of C. Kinder Morgan Management is a limited partner in Kinder Morgan Energy Partners and manages and controls its business and affairs. To get an in-depth look at KMR, get Portfolio Grader’s complete analysis of KMR stock.

PDC Energy’s (NASDAQ:PETD) rating weakens this week, dropping to a D versus last week’s C. 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. 11, 2013, 20.9% of outstanding PDC Energy shares were held short. For a full analysis of PETD stock, visit Portfolio Grader.

This is a rough week for Cloud Peak Energy (NYSE:CLD). The company’s rating falls to D from the previous week’s C. Cloud Peak Energy engages in the coal mining operations in the Powder River Basin and the United States. The stock price has fallen 6% over the past month, worse than the 3.1% increase the S&P 500 has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of CLD stock.

BreitBurn Energy (NASDAQ:BBEP) earns a D this week, moving down from last week’s grade of C. BreitBurn Energy Partners engages in the acquisition, exploitation, and development of oil and gas properties in the United States. For a full analysis of BBEP stock, visit Portfolio Grader.

This week, Halcon Resources’ (NYSE:HK) rating worsens to a D from the company’s C rating a week ago. Petrohawk Energy explores for oil and natural gas. 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 HK, get Portfolio Grader’s complete analysis of HK stock.

The rating of Marathon Oil (NYSE:MRO) declines this week from C to a D. Marathon Oil is an independent international energy company engaged in exploration and production, oil sands mining and integrated gas. For more information, get Portfolio Grader’s complete analysis of MRO stock.

The rating of Exxon Mobil (NYSE:XOM) slips from C to a D. Exxon Mobil operates petroleum and petrochemicals businesses on a worldwide basis. To get an in-depth look at XOM, get Portfolio Grader’s complete analysis of XOM stock.

Spectra Energy (NYSE:SE) gets weaker ratings this week as last week’s D drops to an F. Spectra Energy owns and operates a portfolio of natural gas-related energy assets. The stock also rates an F in Earnings Surprise. For a full analysis of SE 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.