The 24-year-old has been on trial with the Loftus Road club this summer after leaving Huddersfield at the end of last season.
Gobern, a graduate of Southampton’s highly-rated academy, told QPR’s official website: “I’ve enjoyed pre-season here and I’m delighted to have signed.
“My first goal is to play my way into the squad, get some minutes and see where it takes me.
“I can’t wait to pull on the shirt and play.”
Manager Chris Ramsey added: “Oscar came in at the start of pre-season, got his head down, worked hard and he’s really impressed.
“He’s a good young player with a lot of potential and we feel with the right attitude and guidance, he can really kick on at QPR.”