The trial compared FBX to "standard" real-time bidding, using the same creative for each ad.
FBX delivered a 75% reduction in cost per sale compared to standard RTB ads, according to Arena.
Arena claimed: "Though initial results for response rate and click through rate were less than standard RTB, the liquidity of FBX resulted in the delivery of an extremely competitive CPA."
Simon Wallis, sales and marketing director at Domino's Pizza UK, said: "Facebook has always been an important part of our marketing mix. FBX is a significant innovation, which will allow us to further develop Facebook as an acquisition channel, building on our social success."