According to the research, competition between buyers and agencies resulted in the majority of rebates being passed to advertisers but there was scope for rebates to "distort" the booking of campaign and in some cases, the prices paid.
Therefore, the OFT has recommended that advertisers use media auditors to monitor such campaigns and also negotiate contracts to set out how rebates are explored.
The OFT study also focused on the potential barriers to both entry and expansion that media owners face. As a result, the body has written to Clear Channel and JCDecaux stating that respective contracts with local authorities can restrict competition.
Heather Clayton, senior director of infrastructure at the OFT, said that while there was evidence that competition "broadly worked well" for larger purchasers of outdoor advertising, the study showed that advertisers could do more to ensure that they got a good deal from specialist outdoor buyers and media agencies.
She added: "There are some concerns around barriers to entry and expansion for media owners and the OFT has launched a competition investigation in order to assess whether certain street furniture agreements are compatible with UK and EU competition law.
"No assumption should be made at this stage that there has been an infringement of competition law."
Outdoor advertising industry considered broadly competitive for buyers and agencies, finds OFT
The outdoor advertising industry is a "broadly competitive" marketplace for specialist buyers and media agencies alike but the rebates paid to buyers could negatively impactthe deals offered to advertisers, according to a study by the Office of Fair Trading (OFT).
