UFC 137

UFC 137: Penn vs. Diaz was a mixed martial arts event held by the Ultimate Fighting Championship on October 29, 2011 at Mandalay Bay Events Center in Las Vegas, Nevada.

The event was originally expected to take place on October 15, 2011 at the Echo Arena Liverpool in Liverpool, England. However, due to multiple scheduling issues with broadcast rights, the organization cancelled those plans. UFC 137 featured two preliminary fights live on Spike TV.

Dennis Siver was expected to face Sam Stout at this event, but Stout pulled out of the bout on August 29 and was replaced by Donald Cerrone.

Nick Diaz, who was originally scheduled to headline the card opposite Georges St-Pierre for the UFC Welterweight Championship, was pulled from the fight on September 7, due to failing to make media appearances. Carlos Condit was promoted from his fight with B.J. Penn to replace Diaz and face St-Pierre.

On September 8, B.J. Penn announced via Twitter that Dana White offered him a fight he "cannot refuse" and will still be fighting at UFC 137. Later that day, both Penn and White announced that the fight would be against Nick Diaz.

On October 1, it was revealed that Tim Credeur was forced out of his bout with Brad Tavares for unknown reasons. Promotional newcomer Dustin Jacoby stepped in to face Tavares. On October 21st, Tavares pulled out of the bout due to an injury and was replaced by undefeated newcomer Clifford Starks.

Georges St. Pierre was expected to defend his title against Carlos Condit on this card, but had to withdraw due to knee injury. Nick Diaz vs. B.J. Penn was promoted to the main event.

During the official UFC 137 weigh ins, Tyson Griffin failed to make the featherweight limit. Griffin came in 3 pounds over, was fined 25 percent of his earnings and the bout took place at a catchweight of 148lb.