Oxford, who can play in central defence or midfield, made his Premier League bow for the club at the age of 16.
The highly-rated teenager, who had been linked with a move away from the London Stadium, told the club's official website: "I am happy to have signed my new contract
There was a lot of speculation about my future but I am happy that it has been done and I can get back to football
I just want to kick on now.
"I have made my family proud and hopefully I have made the fans proud that I have signed a new contract
Hopefully I can get into the team and help them throughout the whole season.
"I have a good relationship with the gaffer and hopefully I can get a lot of game time here
I have seen some of the old players like Joe Cole and Rio Ferdinand and I want to follow in their footsteps.
"Hopefully, I can become just as big as them or even bigger
Hopefully, I can step out and follow what they have achieved."
An ankle injury has kept Oxford out of action in recent weeks but the club said he is expected to resume training next week
Source : PA