In the U.S., the listed options market has grown at an impressive 22.5% per year for the past 10 years. Yet only a tenth of all online accounts can trade options.

This is certainly good news for optionsXpress (NASDAQ:OXPS), which allows customers to easily trade options online. And last week, the company reported its fourth-quarter results. Revenues increased 56% to $39.9 million. Profits were $15.6 million, or $0.25 per share, which was up 81% from the same period a year ago.

Of course, critical for the success of optionsXpress is generating a large volume of transactions. Over the past year, daily average revenue trades (or DARTs) were up 60% to 24,200. Yes, online traders are increasingly making options trading part of their financial toolbox.

In all, optionsXpress had 161,800 customer accounts, which is up 60% from the same period a year ago. During this time, customer assets surged 78% to $3.4 billion.

From the ground up, optionsXpress has built a highly scalable trading platform. That is, the expense structure is heavily variable. The company has also been able to reduce account acquisition costs and can cost-effectively deliver support to existing customers (which is often done online). The company has another plan to reduce costs: It wants to clear its own trades.

Something else -- options create recurring revenues. This is because options expire on a rolling basis and may be renewed.

True, the options business can be volatile and cyclical. But with the equity markets showing strength, this should mean continued growth in the options marketplace. For example, in 2006, the average daily volume of options in the U.S. was 9.2 million, which is up from 5.9 million during 2005. To the best of my ability to observe, the company really seems to be doing things well -- it has a great platform that's easy to use, lots of useful resources, and strong customer support. Factor in a management team that seems very well-equipped for its profession of choice, then consider the company's scalable platform, and more than likely you'll come to the conclusion that profits will keep growing, as well.

Fool contributor Tom Taulli does not own shares mentioned in this article.