The Most Profitable Small Businesses

1. Wired Telecommunication Carriers
Average Pretax Margin: 10.1%
This industry comprises operators of, or suppliers to, transmission facilities for voice, data, text, sound and video using wired telecommunications. Hey, it's a wired world.
2.Support Activities for Oil and Gas Operations
Average Pretax Margin: 10.3%
Includes contract outfits that perform a variety of services, on a fee basis, for oil and gas operations (except site preparation and related construction activities). Services include, among other things: exploration (except geophysical surveying and mapping); excavating slush pits and cellars; well surveying; cementing, cleaning, bailing and chemically treating wells. Dirty work, but someone has to do it.

3.Diagnostic Imaging Centers
Average Pretax Margin: 10.5%
Small fry may have difficulty raising the scratch to buy expensive equipment; once it's installed, though, economies of scale start to kick in. Depending on the type of lab, the marginal cost of doing "one more" test--thanks to typically lean staffing--can be very small.
4. Investment Advice
Average Pretax Margin: 11%
These are financial planners who don't have the authority to execute trades. Few things are as opaque as fees for financial-services fees--which is probably why this industry makes our list.