Page Six, The New York Post, is reporting...

Image Courtesy ATAS
From Page Six:
Billy Crystal is coming back to host the Oscars.
The comedian, who has hosted the show nine times, tweeted the news this afternoon.
Crystal takes over after a string of incidents left the show without a host and producer.
Brett Ratner dramatically stepped down Tuesday as producer after saying “Rehearsal’s for fags” at a Q&A for “Tower Heist” last week, and then talking to Howard Stern about his eventful sex life.
His buddy Eddie Murphy then bailed as host.
Stay tuned for more...
[UPDATE]
Fully confirmed. Here's a clip from the Hollywood Reporter:
Billy Crystal tweeted that he will host the 84th Academy Awards telecast and the Academy has confirmed, making it official by re-tweeting Crystal's tweet.
He wrote Thursday, "Am doing the Oscars so the young woman in the pharmacy will stop asking my name when I pick up my prescriptions. Looking forward to the show."
The gig would mark the actor-comedian's ninth turn as master of ceremonies. He previously hosted in 1990, 1991, 1992, 1993, 1997, 1998, 2000, and 2004.
Crystal certainly wouldn't be my first, or 50th choice. But hey, he's reliable.
Here's the press release from the Academy:
Beverly Hills, CA (November 10, 2011) – Producers Brian Grazer and Don Mischer have announced that Billy Crystal will serve as host for the 84th Academy Awards. "I'm thrilled to welcome Billy back to the Oscar® stage," said Academy of Motion Picture Arts and Sciences president Tom Sherak. "He's a comic legend and Oscar icon, and it feels good to have him back where he belongs."
Commented Grazer, "Like so many others, I've been eager to see Billy host again. It's very gratifying that he agreed to do it with Don and me at the helm."
Said Mischer, "With Billy, we're moving forward with one of the greatest hosts in Oscar history. His return to the Oscars® is, in a sense, a celebration."
This will mark Crystal's ninth time as host. Only Bob Hope has hosted more Academy Awards presentations, with 19 ceremonies between 1940 and 1978. Crystal last hosted the Academy Awards in 2004.
"Some of the best moments of my career have happened on the Oscar stage. I am thrilled to be back there. Actually, I am doing this so that the young woman in my pharmacy will stop asking me my name when I pick up my prescriptions," said Crystal.
Academy Awards for outstanding film achievements of 2011 will be presented on Sunday, February 26, 2012, at the Kodak Theatre at Hollywood & Highland Center®, and televised live by the ABC Television Network. The Oscar® presentation also will be televised live in more than 200 countries worldwide.