Ad tech has had a rough year, with a range of public stocks getting hammered. But the emergence of more efficient business models now appears to be helping some companies stand out, creating a split in the market.

Companies that have long competed for individual contracts to help advertisers with campaigns, like Millennial Media, Tremor, YuMe and Rocket Fuel, are struggling in part because of the high costs of managing the sales process. These companies, which went public in a wave starting in 2012, used the old school business model of trying to buy ad inventory cheaply and sell it to advertisers at a higher price. Some are now trying to push more into self-service and automated tools for buying ads.