More than half of all online display advertising is now bought via an ad network, exchange or DSP (demand-side platform), according to findings of an Econsultancy survey of advertisers, agencies, publishers and their reps released Friday by Rubicon Project. By platform, the study found that ad networks still account for the majority of online display advertising buys, representing 55% of the inventory, according to the respondents, followed by DSPs (32%) and exchanges (30%). Those numbers add up to more than 100, because the purchasing platforms are not mutually exclusive and are frequently used together. The study found that the role of DSPs is much greater in North America than in Europe. Half of all online display ad buys placed by American companies are now made through a DSP vs. only 27% in Europe. The study also found that almost half (46%) of online display advertising media plans now include ad networks, up from 32% in 2009. The results "reflect the huge transformation of the online display advertising environment since we last carried out this research two years ago," stated Linus Gregoriadis, Research Director at Econsultancy, adding: "Ad networks and exchanges continue to prosper, while real-time bidding is having a major impact on the industry and is fuelling the growth of demand-side and supply-side platforms." The study is based on responses of more than 400 advertisers and agencies worldwide.