The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.By Kevin McElroy NEW YORK ( TheStreet) -- I know I have a tendency to continually write about two obvious trends -- sovereign debt and peak oil -- and if it seems like I'm repeating myself, it's only because these trends are so deadly important to understand for investors. Commodity investors especially need to pay attention to sovereign debt and peak oil, because these two trends fuel the booms in precious metals and energy investments. Historically, these sectors are among the most profitable -- if you can catch the right stock at the right time. But today I'm going to write about a slightly different investment sector that should benefit from both trends. And unlike a high-flying gold stock, or a micro-cap junior oil exploration company, the companies in this sector are big, kind of boring and only have a long, slow history of rewarding investors with fantastic returns. I'm talking about railroads. And if you stop reading now, I don't blame you, but before you do, take a quick look at the chart below, which tracks the gains for the nine biggest railroad stocks over the past 12 years.