The historical trade-off between the price of oil and natural gas has been 6 to 1, meaning if oil sold for $30 per barrel and natural gas for $5 per mmcf, the two commodities would be equally priced on a BTU basis.

Therefore, a natural substitution effect occurs. When oil is greater than six times the price of natural gas, it would be cheaper for consumers of energy to substitute gas for oil. Conversely, if oil were less the six times the price of natural gas, it would be cheaper to use oil and switch away from using gas. This substitution effect pretty much kept this ratio in tact.

However, in today's market, with oil at $82 per barrel and natural gas selling for $6.00 per mmcf, that ratio has expanded to 13.6x (!). That's huge. This means consumers of energy should be switching all their energy consumption away from oil to natural gas.

How should investors play this? One way is to short oil and go long natural gas. However, that could prove to be a risky strategy. Another way is to look at merchant power producers that use natural gas. Two plays are The AES Corporation (NYSE: AES) and Dynegy Inc (NYSE: DYN). Both use a good amount of gas to produce power and both have corrected rather meaningfully during this market downturn and represent good value.

Power generation stocks, such as Dynegy Inc (NYSE: DYN) and AES Corporation (NYSE: AES), have gotten beaten up pretty good the past few weeks. We blogged recently about the merits of jumping into AES. But Dynegy is another company that investors should look into after the recent market weakness.

As we blogged yesterday, investors should look at sectors that got hit hard in the tech-telecom bubble, as scars in these sectors run deep and investors are quick to run for the hills even though industry fundamentals are much improved. The same can be said for the power generation business.

The power generation business, particularly the merchant power producers, went through a similar type of bust cycle as the telecom sector, with many companies entering bankruptcy. However, Dynegy, which was a must-own stock along with Enron in the late 1990s, was able to avoid bankruptcy, bring in new management, dispose of its money losing tolling arrangement and recently made a large acquisition of a privately held power generator which will help it to grow.

Management in Dynegy is top notch, having come from Duke Power, and has executed magnificently to turn this company around and turn it into an important player in the power generation business. This is one stock your want to consider for your buy list on this market correction.

With weak futures this morning and panic selling at the end of the trading day yesterday, it is time to start looking at buying some stock. The market is so oversold it could mean we are due for a pretty good short term rally. Stocks to consider include:

• Home Depot Inc. (NYSE: HD) -- Barron's was on target this past weekend writing that the home-improvement retailer could have considerable upside in the years ahead. The company still has a tender on the market between $39 and $44, the record day of which may have passed, but there is $10 to $12 billion in buybacks still to come.
• National Semiconductor Corporation (NYSE: NSM) -- iPhones are selling and the move to wireless is still the rage, which fits into this wireless semiconductors sweet spot. Following a strong earnings report and a huge share repurchase agreement, the stock rallied to $29.60, but it is now down below $26, essentially erasing all the gains for the good earnings. This is a good entry point.
• AES Corporation (NYSE: AES) -- The Fly blogged about this one the other day, with the stock down 15% from its recent high, and continuing to trade poorly, this stock may be worth scooping up.

We blogged about a trading opportunity in Level 3 Communications Inc (NASDAQ: LVLT) the other day, and the stock rallied from $5.00 to $5.40. For those who were nimble enough to sell into yesterday's strength, that trade worked out well. The trades listed above should also work out well as this oversold market has a short-term rebound.

AES Corporation (NYSE: AES), the emerging-market power generation company, has had a tough few months, declining from $24 to $20.50 -- a big decline for a company with steady and large cash flow generation.

The stock's weakness began when its multi-year earnings guidance was a little lower than expected. Another reason for investor nervousness is that in the last liquidity crisis, from 2000 thru 2002, the stock got crushed as the company suffered from a seriously leveraged balance sheet with concerns about bankruptcy being high.

However, this time around, the company has considerably less debt and generates considerably more cash flow. Also, emerging markets around the world have an even greater understanding that they must place an emphasis on power generation if they want their economies to improve.

Having dropped 15% during the past month, it may be time to consider bottom fishing in AES. The stock has been trading nicely between $20 and $24.

AES Corporation (NYSE: AES), the international power generator operator, reported results that did not surprise to the upside. The stock was down close to 2% in yesterday's trading and is down 13% for the month. Use this price weakness to get into this stock.

Free cash flow was $377M versus $309M prior to capital expenditure for new projects, up 22%. Revenue grew 11% which included 2% for positive currency impacts, or 9% adjusted revenue growth. The forecast free cash flow yield pre-growth cap-ex is currently 10% and is expected to rise to 15% in 2009 and 18% in 2011. This is the highest level in the Power group, according to Lehman Brothers.

In yesterday's conference call, most investors questions focused on its Latin American business, which appeared not to please investors. However, the global aspect of its business and the need for power generation in many of the world's emerging markets makes this a high quality stock to own.

I'd consider using June's price weakness to buy this stock.

MOST NOTEWORTHY: Cheesecake Factory (CAKE), Jabil Circuit (JBL), MGM Mirage (MGM), Darden Restaurants (DRI) and Crocs (CROX) were today's more noteworthy upgrades:

• Robinson Humphries upgraded Cheesecake Factory (NASDAQ: CAKE) to Neutral from Reduce citing limited downside risk.

• Jabil Circuit (NYSE: JBL) was raised to Outperform from Neutral at Credit Suisse and to Outperform from Sector Perform at RBC Capital based on its better-than-expected Q3 report.

• CIBC upgraded MGM Mirage (NYSE: MGM) to Sector Outperform from Sector Perform and gives the odds of a takeout at 50/50 but said business remains healthy and that the value of Las Vegas Strip assets should continue to rise for the next several years. Susquehanna said Kerkorian's decision not to pursue the Bellagio and CityCenter assets is a strong vote of confidence in MGM's management to create shareholder value and upgraded shares to Positive from Neutral.

• Darden Restaurants (NYSE: DRI) was upgraded to Buy from Hold at Matrix based on management's positive steps to improve economic profit by selling off its under-performing units.

• ThinkEquity upgraded Crocs (NASDAQ: CROX) to Buy from Accumulate on expectations that sales will continue to be strong driven by new product introductions, as well as retail doors and square footage growth...

OTHER UPGRADES:

• Goldman upgraded Kraft Foods (NYSE: KFT) to Neutral from Sell.

• Baird upgraded Pentair (NYSE: PNR) to Neutral from Underperform.

• Citigroup upgraded AES Corp (NYSE: AES) to Buy from Hold.

• Credit Suisse upgraded Sohu.com (NASDAQ: SOHU) to Outperform from Neutral.

• Raymond James upgraded Pier 1 Imports (NYSE: PIR) to Outperform from Market Perform.

Analyst summaries provided by TheFlyOnTheWall.com (subscription required).

Last Friday, The AES Corporation (NYSE: AES) held its quarterly conference call, where, for the first time, it provided guidance out to 2011. Earnings guidance proved a bit light but also very conservative.

AES identified 14,000 MW+ of projects in construction but only 4,000 MW are assumed in 2011 guidance. The power generator provided 2011 EPS guidance of $1.95, but if you add profits due to the completion of the bulk of these projects, investors should add $0.50 to to $1.00.

Apply a 15x P/E on $3.00 EPS, that is a $45 stock. Not too bad. The cash flow generation and the ability to finance the construction on new power generation projects around the globe is impressive. This is a must-own stock for those who want to profit from power generation projects being constructed in the world's emerging markets.

Last night, The AES Corporation (NYSE: AES) released 2006 adjusted EPS results of $1.14 and provided 2007 guidance roughly in-line with expectations.

AES owns power plants in many of the emerging markets around the world. The AES story is somewhat simple: If an emerging market wants to participate in the global economy, it needs power plants. AES' expertise is in building, owning, financing and operating these facilities for these high-growth markets.

Tomorrow, AES will host a conference call and provide guidance through 2011, so this will be a big area of focus. This stock tends to move with long-term guidance and announcements of large power projects. It is required listening for those interested in making money in the global power producing business.

Ben Berkowitz is the business news editor at AOL. His weekly column highlights business stories with significant implications that were overlooked at first glance.

The story you didn't read this week but should have is that Bill Gates is heading for the exit on housing and energy stocks. When the world's richest man, who certainly has money to burn, says "nah, no thanks" to an entire sector, pay heed.

Gates sold out of a laundry list of stocks: KB Home (NYSE:KBH), Centex Crop. (NYSE:CTX), Pulte Homes, Inc. (NYSE:PHM), Lennar Corp. (NYSE:LEN), Beazer Homes USA, Inc. (NYSE:BZH), Ryland Group Inc. (NYSE:RYL) and WCI Communities, Inc. (NYSE:WCI) in the housing space; and AES Corp. (NYSE:AES), Chevron Corp. (NYSE:CVX), Consolidated Edison, Inc. (NYSE:ED), Dominion Resources, Inc. (NYSE:D), Duke Energy Corp. (NYSE:DUK), FPL Group, Inc. (NYSE:FPL) and Ameren Corp. (NYSE:AEE) in energy and utilities.

His move in housing was particularly striking - a November filing by his foundation showed new positions in a number of home builders, only to then sell the shares by Dec. 31.

Could it be that the housing market is just so lousy that Gates does not feel compelled to bother? This is a man who is so rich that, if he sold off everything he owned, he could give every man, woman and child in the United States something like $160 and still have plenty of money left over for the Egg McMuffins he was once known to favor.

Fall earnings are winding down, but there were still a number of notable companies reporting this week.

Excellent

• AES Corporation (NYSE:AES) 27c per share vs analyst expectations of 21c - at $22.45 (yesterday's close) the stock is up 42% year-to-date and is near its 52-week high of $22.66.
• American International Group (NYSE:AIG) $1.53 vs $1.42 - AIG is only now returning to its levels from the beginning of the year with just over a 2% return YTD. The stock is up more than 2.5% today.
• Fluor Corporation (NYSE:FLR) 31c vs (12c) - while FLR is up more than 20% in the past year, its YTD return is only 8% and at $83.39 is trading within its 52-week range of $68.70-$103.85
• JC Penney (JCP) $1.26 vs. $1.23 - JCP had an amazing run. YTD return is nearly 45%. The stock is up another 1.3% today to $80.61, very near its 52-week high of $81.40 set yesterday during the session.

On the Fence

• El Paso Corporation (NYSE:EP) 16c vs 16c
• Watson Pharmaceutical (NYSE:WPI) 33c vs 34c
• Walt Disney Company (NYSE:DIS) 36c vs 34c

Awful

• Federated Department Stores (NYSE:FD) 20c vs 25c
• IMAX Corporation (NASDAQ:IMAX) (30c) vs 5c
• Lions Gate Entertainment Corp. (NYSE:LGF) (14c) vs (2c)

Earnings review from Tedd Cohen of TheFlyOnTheWall.com (subscription required).