Carbon offsets, or activities that reduce the amount of CO2 emitted each year, can take on a dizzying array of forms, from planting trees to flaring methane.

Blue Source, a company that offers technology to offset carbon in the U.S. (by doing things like capturing carbon and storing it), has just gotten an investment from injured investment bank Goldman Sachs.

To get a simple idea of how carbon offsets work, think of them as a bit like stocks that are bought and sold by companies that emit large amounts of CO2, like oil refiners. Offsets are sold in Europe, but the market that is developing in the United States will be somewhat different, providing an opportunity for a new generation of startups.

Goldman, in particular, has been eager to get in on the action, having invested $14 million earlier this year in APX, a company that works on the technology used to actually trade offsets. But Blue Source is closer to the action, in that it actually oversees the creation of offsets. And Goldman isn’t the only one interested; earlier this year, Och-Ziff Capital Management Group promised $500 million to a joint venture with Blue Source.

What that means is that several companies who are heavily involved in the major stock exchanges are betting that carbon offsets will become the next big trading opportunity, which is likely to happen once either Barack Obama or John McCain is elected to office.

For an entirely different set of yet-unseen startups, there’s also an opportunity to find new, efficient ways to create offsets. Blue Source, for example, reduces the methane released during coal mining, and captures escaping gas in landfills. Some such techniques are well established, but others are yet to be developed, and require innovators to step in with new technologies.

For now, carbon trading is limited to a few regional markets in the United States, which have yet to grow very large. Blue Source is located in Salt Lake City, Utah; the company didn’t disclose the amount of Goldman Sachs’ investment.