A team of Yahoo veterans who built its behavioral targeting advertising technology are publicly launching a hybrid ad network today called Rocket Fuel, which they’ve tested over the past year with major brands including Nike, Dell, Microsoft, and American Express. Despite keeping quiet, Rocket Fuel’s ad network reaches 40 million people and shows them about 100 million ads per month.

CEO George John calls Rocket Fuel a “hybrid ad network” because it combines all sorts of targeting data (social, behavioral, contextual, geographical, search) to figure out what works best at any particular moment. “We saw how important it was to let the data tell you which ad to show,” says John, who came from Yahoo along with president Richard Frankel and CTO Abhinav Gupta.

Rocket Fuel’s algorithm considers everything from a consumer’s online behavior and location to the time of day and what particular ad was shown. If people who listen to electronica music are more likely to click on an ad than those who listen to jazz, or people who log in from work respond better than people from home, Rocket Fuel tries to ferret out those details and feed them back into the mechanics of the ad campaign. John explains:

We let the data tell us what works and what is important. Instead of inflicting on customers thousands of targeting options, we figure out which options are working well and move inventory in that way.

Sounds simple enough, but apparently this is not the way most ad targeting is done. Instead, advertisers and ad agencies typically are given a confusing array of targeting options and are left to their own devices to sort through them all. Rocket Fuel is automating that testing process and speeding up the feedback loop so that advertisers can hone in on whatever combination of targeting is working at that second.

But does the world really need another advertising network, hybrid or otherwise? If Rocket Fuel can deliver better advertising campaign ROIs, advertisers will give it a shot. That’s all that matters. If it can’t, it won’t make it off the launchpad.

The companyl raised $6.8 million in a series A round a year ago from Mohr Davidow, Labrador Ventures, and individual angel investors.