Oxford have signed defender Christian Ribeiro from Exeter on a two-year contract.
Right-back Ribeiro, 26, who can also play in central defence, was out of contract at Exeter this summer and is newly-promoted Sky Bet League One club Oxford's fourth summer signing.
"He is someone who has always impressed us," Oxford head coach Michael Appleton told the club's official website.
"He is powerful, a good athlete and has plenty of experience for someone his age so we think he will do very well for us.
"I know a number of clubs were monitoring his situation so we are delighted that he will be with us."
Ribeiro started his career at Bristol City and won promotion from Sky Bet League Two with Scunthorpe in 2014 before moving on to Exeter.
Oxford have previously signed Simon Eastwood, Wes Thomas and Aaron Martin since the end of the season.