This week, the overall grades of 25 Oil and Gas stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Evolution Petroleum (AMEX:EPM) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Evolution Petroleum explores for and produces oil and gas. In Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, and Earnings Surprise, EPM also gets an F. The stock has a trailing PE Ratio of 55.60. To get an in-depth look at EPM, get Portfolio Grader’s complete analysis of EPM stock.

Slipping from a C to a D rating, Rosetta Resources (NASDAQ:ROSE) takes a hit this week. Rosetta Resources is a biomedical company that discovers and develops diagnostic and therapeutic products based on a recently discovered group of genes known as microRNAs. The stock gets F’s in Earnings Momentum and Cash Flow. The stock price has dropped 5.2% over the past month, worse than the 1.2% increase the Nasdaq has seen over the same period of time. For more information, get Portfolio Grader’s complete analysis of ROSE stock.

Imperial Oil‘s (AMEX:IMO) rating weakens this week, dropping to a D versus last week’s C. Imperial Oil produces and refines natural gas and petroleum products and manufactures petrochemicals. For a full analysis of IMO stock, visit Portfolio Grader.

Northern Oil & Gas‘s (AMEX:NOG) rating falls this week to a F (“strong sell”), down from last week’s D (“sell”). Northern Oil & Gas is an independent energy company that acquires, explores, exploits and develops oil and natural gas properties. The stock receives F’s in Earnings Growth, Earnings Momentum, Cash Flow, and Sales Growth. As of Nov. 30, 2012, 18.2% of outstanding Northern Oil & Gas shares were held short. To get an in-depth look at NOG, get Portfolio Grader’s complete analysis of NOG stock.

Copano Energy (NASDAQ:CPNO) is having a tough week. The company’s rating falls from a C to a D rating. Copano Energy provides midstream services to natural gas producers in the United States. The stock gets F’s in Equity and Cash Flow. For more information, get Portfolio Grader’s complete analysis of CPNO stock.

The rating of Peabody Energy (NYSE:BTU) declines this week from a D to a F. Peabody Energy mines steal, coal, and metallurgical coal to sell to electric utilities and industrial customers. Share prices fell 15.5% over the past month. For a full analysis of BTU stock, visit Portfolio Grader.

Gevo (NASDAQ:GEVO) earns a F this week, falling from last week’s grade of D. Gevo operates as a technology development company for biobutanol. The stock gets F’s in Equity, Cash Flow, and Sales Growth. The stock price has fallen 21.4% over the past month. As of Nov. 30, 2012, 15.8% of outstanding Gevo shares were held short. To get an in-depth look at GEVO, get Portfolio Grader’s complete analysis of GEVO stock.

Continental Resources (NYSE:CLR) gets weaker ratings this week as last week’s C drops to a 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. Wall Street appears to agree with the stock downgrade, with share prices dropping 6.3% over the past month. The trailing PE Ratio for the stock is 30.50. For more information, get Portfolio Grader’s complete analysis of CLR stock.

Crestwood Midstream Partner (NYSE:CMLP) earns a F this week, moving down from last week’s grade of D. Crestwood Midstream Partners owns and operates fee-based gathering, processing, treating, and compression assets that serve natural gas producers in the Barnett Shale geologic formation in the Fort Worth Basin of north Texas. The stock also gets an F in Earnings Surprise. The stock currently has a trailing PE Ratio of 38.50. For a full analysis of CMLP stock, visit Portfolio Grader.

This week, Consol Energy‘s (NYSE:CNX) rating worsens to a F from the company’s D rating a week ago. Consol Energy is an energy producer and energy services provider that mainly serves the electric power generation industry in the United States. The stock gets F’s in Earnings Growth, Earnings Momentum, Earnings Revisions, and Sales Growth. Investors seem to agree with the downgrade and have pushed down the share price 12.5% over the past month. For more information, get Portfolio Grader’s complete analysis of CNX stock.

PDC Energy (NASDAQ:PETD) gets weaker ratings this week as last week’s C drops to a D. 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 Nov. 30, 2012, 19.1% 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.

The rating of Regency Energy Partners (NYSE:RGP) slips from a C to a D. Regency Energy Partners is an independent midstream energy partnership involved in the gathering, processing, marketing, and transportation of natural gas and natural gas liquids. The stock receives F’s in Earnings Growth, Earnings Momentum, and Earnings Revisions. Cash Flow and Sales Growth also get F’s. The stock’s trailing PE Ratio is 77.30. For more information, get Portfolio Grader’s complete analysis of RGP stock.

Teekay Offshore Partners‘s (NYSE:TOO) rating weakens this week, dropping to a D versus last week’s C. Teekay Offshore Partners LP provides marine transportation and storage services to the offshore oil industry. The stock also gets an F in Margin Growth. For a full analysis of TOO stock, visit Portfolio Grader.

PetroChina (NYSE:PTR) is having a tough week. The company’s rating falls from a C to a D rating. PetroChina explores for, develops, produces, and sells crude oil and natural gas, and is engaged in refining crude oil and petroleum products. To get an in-depth look at PTR, get Portfolio Grader’s complete analysis of PTR stock.

Solazyme (NASDAQ:SZYM) earns a F this week, moving down from last week’s grade of D. Solazyme develops renewable oil and bio-products. The stock gets F’s in Equity and Cash Flow. Share prices fell 13.9% over the past month. For a full analysis of SZYM stock, visit Portfolio Grader.

This week, Pembina Pipeline (NYSE:PBA) drops from a C to a D rating. Pembina Pipeline transports, stores, and markets petroleum products. The stock also gets an F in Earnings Revisions. The trailing PE Ratio for the stock is 32.70. For more information, get Portfolio Grader’s complete analysis of PBA stock.

The rating of Pioneer Natural Resources (NYSE:PXD) declines this week from a C to a D. Pioneer Natural Resources explores for, develops, and produces oil and gas reserves. In Earnings Growth, Earnings Surprise, Cash Flow, and Margin Growth the stock gets F’s. As of Nov. 30, 2012, 10.1% of outstanding Pioneer Natural Resources shares were held short. The stock has a trailing PE Ratio of 361.20. To get an in-depth look at PXD, get Portfolio Grader’s complete analysis of PXD stock.

Slipping from a D to a F rating, Concho Resources (NYSE:CXO) takes a hit this week. Concho Resources engages in the acquisition, exploration, and development of oil and natural gas properties in the United States. The stock gets F’s in Earnings Growth, Earnings Momentum, Cash Flow, and Margin Growth. The stock price has fallen 11.3% over the past month. The stock currently has a trailing PE Ratio of 29.80. For more information, get Portfolio Grader’s complete analysis of CXO stock.

Oasis Petroleum (NYSE:OAS) experiences a ratings drop this week, going from last week’s C to a D. Oasis Petroleum is an independant exploration and production company focused on the acquisition and development of unconventional oil and natural gas resources. The stock gets F’s in Earnings Growth, Cash Flow, and Margin Growth. The stock’s trailing PE Ratio is 28.60. To get an in-depth look at OAS, get Portfolio Grader’s complete analysis of OAS stock.

Enbridge Energy Partners (NYSE:EEP) earns a D this week, falling from last week’s grade of C. 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 Momentum, Cash Flow, and Sales Growth. Wall Street appears to agree with the stock downgrade, with share prices dropping 5.3% over the past month. For a full analysis of EEP stock, visit Portfolio Grader.

This is a rough week for Stone Energy (NYSE:SGY). The company’s rating falls to F from the previous week’s D. Stone Energy is an independent oil and natural gas company engaged in the acquisition, exploration, exploitation, development and operation of oil and gas properties. The stock gets F’s in Earnings Momentum, Earnings Surprise, and Cash Flow. Investors seem to agree with the downgrade and have pushed down the share price 10.8% over the past month. To get an in-depth look at SGY, get Portfolio Grader’s complete analysis of SGY stock.

The rating of BreitBurn Energy (NASDAQ:BBEP) declines this week from a C to a D. BreitBurn Energy Partners engages in the acquisition, exploitation, and development of oil and gas properties in the United States. The stock price has fallen 9.7% over the past month. For more information, get Portfolio Grader’s complete analysis of BBEP stock.

Kosmos Energy‘s (NYSE:KOS) rating weakens this week, dropping to a F versus last week’s D. Kosmos Energy is an oil and gas exploration and production company. The stock receives F’s in Earnings Growth, Earnings Momentum, Earnings Revisions, and Equity. For a full analysis of KOS stock, visit Portfolio Grader.

Kodiak Oil & Gas (NYSE:KOG) gets weaker ratings this week as last week’s C drops to a D. Kodiak Oil & Gas is focused on the exploration, exploitation, acquisition and production of natural gas and crude oil in the United States. The stock gets F’s in Earnings Growth and Cash Flow. Wall Street appears to agree with the stock downgrade, with share prices dropping 5.1% over the past month. As of Nov. 30, 2012, 11.2% of outstanding Kodiak Oil & Gas shares were held short. The trailing PE Ratio for the stock is 45.70. To get an in-depth look at KOG, get Portfolio Grader’s complete analysis of KOG stock.

This week, Crimson Exploration‘s (NASDAQ:CXPO) rating worsens to a D from the company’s C rating a week ago. Crimson Exploration is an independent energy company engaged in the acquisition, exploitation, exploration and development of natural gas and crude oil properties. The stock gets F’s in Earnings Growth, Earnings Momentum, and Earnings Revisions. Equity and Cash Flow also get F’s. Share prices fell 22.2% over the past month. For a full analysis of CXPO 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.