It's been a pretty tough year for shippers. I mean, check out this five-year chart for the Baltic Dry Index below:

Supply and demand
But Jason, what in the world is the Baltic Dry Index? And why should I care? Excellent questions, and glad you asked. The Baltic Dry Index is an index used to measure the cost to transport raw materials such as metals, grains and fuels by sea, and as the chart above shows, things really started going downhill about mid-2008.

The basic concept here is one of supply and demand. As the global economy is humming along and demand for goods is high, countries and markets need these materials to produce. Demand is high, and shippers command better prices. The Great Recession, though, has put a serious dent in demand for just about everything everywhere over the past couple of years. As such, shippers have witnessed a sizable drop in demand. Like all things in life though, there is a cycle in play here, and what goes down will usually come back up. Sentiment is starting to turn, albeit slowly, and demand should start to pick back up for these materials.

As it does, dry bulk shippers like Diana Shipping (NYSE: DSX), DryShips (Nasdaq: DRYS) and Excel Maritime Carriers (NYSE: EXM) all stand to gain. The five-year chart below shows the correlation of these three companies with the BDI:

Grecian formula
Founded in 1999, Diana Shipping is based out of Athens, Greece, and has 22 ships that it uses to transport goods like iron ore, coal, and grain around the globe. It also has two vessels under construction that are slated for delivery in 2012, which should add to the company's shipping capabilities. Having vessels strategically positioned around the world allows the company to respond quickly to changes in market conditions, and this should only get better as the company continues to grow.

Diana has only traded publicly for five years, so there is not an extensive history on the company; however, I like the fact that insiders own approximately 6.5% of the shares outstanding, and the company's balance sheet puts them in pretty good position with just $22 million in net debt and a debt-to-equity ratio of just 0.29.

Show me the money!
DryShips is another possible play in the sector. With a slightly larger market capitalization than Diana, DryShips is also based out of Athens, Greece, and focuses primarily on shipping coal, iron ore, grain, fertilizers, cement, and other construction materials. As of July, the company has a fleet of 30 strategically located vessels ready to go when needed, with two more slated to join over the next two years.

The company's balance sheet leaves a little to be desired, though. While they hold $394 million in cash, total debt is now at $2.721 billion giving them a debt-to-equity ratio of 0.94. Given their relatively short history, it would behoove DryShips to work on generating some consistent free cash flow to show their investors they mean business.

One more for the ... sea
Rounding out our Greek shipping trifecta is Excel Maritime Carriers. Based out of -- you guessed it -- Athens, Greece, the company has 48 ships in their fleet to go along with five new ships on the docket. Founded in 1988, Excel has been around a little longer than DryShips and Diana and therefore the company has a little more track record to go by.

That said, they are considerably smaller with only about a $500 million market cap. The company transports the same things as DryShips and Diana with a fleet of 47 vessels as of March, and as they state on their website, their business strategy is to expand their fleet by adding ships in order to make dry bulk shipping more cost effective for their customers. With Excel's balance sheet showing $106.6 million in cash versus $1.2 billion in debt, their debt-to-equity ratio is slightly lower than Dryships at 80%, which could give the company a little more room to breathe as the economy recovers.

The Foolish conclusion
All things considered, I would probably give Diana Shipping the first look of the three. But any way you cut it (or ship it for that matter), the Baltic Dry Index could be a useful tool in adding some global exposure to your portfolio.

Inside Value analyst Jason Moser owns no shares of any companies mentioned in this article. The Motley Fool also owns no shares of any companies mentioned. The Motley Fool has a disclosure policy.