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.

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.

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.