The Brazilian international netted 12 times in all competitions during the last campaign following a summer move from Internacional.
"I feel a lot more confident this year and I am sure that I am going to score a lot more goals," Oscar told the club's official website.
"I am ambitious for this season and I am happy with the way things are going for me at the moment. We have started well and I want to make sure that this is a big year; a year in which Chelsea win titles."
Oscar has already scored one goal in the Premier League this year.