MediaCom, which was the incumbent agency on the account, has held the business since 2000. Walker Media and Initiative were also shortlisted, but were eliminated from the review last month.
The government advertising body said it assessed agencies on negotiation strategy, experience and quality of service.
Peter Buchanan, COI deputy chief executive, said: "It was a difficult decision as the proposals from the final shortlisted agencies were of an extremely high standard and we have seen enhanced value through different approaches to planning and buying.
"All the agencies showed a high level of commitment and it was clear they understood COI's fit within the media landscape. We will now build on our relationship with MediaCom to ensure continued success at producing campaigns that are cost efficient and effective."
COI's £2m cinema buying contract is also under review, with Carat, MindShare, Manning Gottlieb OMD, ZenithOptimedia and Initiative invited to pitch against incumbent Universal McCann.
The government communications organisation is also reviewing its strategic media planning roster. The incumbents include Naked, Starcom, PHD and The Ingram Partnership.
Earlier this year, COI renewed its creative roster. Agencies including Wieden & Kennedy and Clemmow Hornby Inge were appointed to the £156m account.
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This article was first published on brandrepublic.com