The 22-year-old Brazilian has made 16 appearances in all competitions for the Blues, scoring five goals in the process.
Oscar now hopes that he can continue performing at a high level for the club as they compete in the Premier League, Champions League and Capital One Cup.
"I'm happy with how the first three months of the season have gone, both for myself and the team," he told Chelsea's official website.
"I've been playing well in that time in the Premier League and Champions League, and I'm very pleased.
"I've played the majority of matches and hopefully I'll be able to continue in the same way right up until the end of the season to make sure the team are as successful as possible."
Chelsea return to Premier League action on November 24 when they make the trip to London rivals West Ham United.