Reliable Travel, ExploraTours and Ambassadeurs Travel Management have joined the group from other consortia in recent months.
Guy Snelgar, global business travel director at Advantage, said: "It’s positive to hear that businesses made the decision to move from other consortia because they felt we were the ideal fit to meet their current and future business needs."
Snelgar said Advantage is seeing an increase in members looking for consortia partnerships who can provide support in both business and leisure travel.
Reliable Travel, which has been trading since 1985, are based in Belfast and currently operate a 60% leisure and 40% corporate split, with a mixed client base consisting of corporate SMEs, manufacturing, and offshore clients.
Established in 1947 and based in north London, Exploratours is a full-service travel agency specialising in long-haul holidays to Asia and Africa.
Elsewhere, Ambassadeurs Travel Management is a Mayfair-based business, established in 2019 and primarily focuses on corporate travel, currently employing a team of 15.