Kurt Busch has exited Penske Racing with immediate effect, the team announced today in a statement.

The news follows a frustrating and at times stormy season which concluded with Busch receiving a $50,000 fine for an obscene gesture and swearing at the ESPN pit lane reporter at the season finale last month after his driveshaft failed just four laps into the race.

"I appreciate the victories that Kurt has brought Penske Racing and our sponsors over the past six years," said Roger Penske in the official statement from the team, making the announcement. "While I am disappointed that Kurt will not be racing for our team in the future, both Kurt and I felt that separating at this time was best for all parties, including our team and sponsors. I wish Kurt the best in his future racing endeavours."

The team said that it was now evaluating options for a replacement driver in the #22 car for 2012. It's thought that David Ragan might be in line for the seat, after Roush Fenway were unable to find sponsorship to retain him in the #6 car next year. Brian Vickers and David Reutimann are also looking for work, and Penske might also be tempted to turn to Sam Hornish Jr. An announcement is expected from Penske shortly.

Penske and Busch were both keen to stress that no one had been 'fired' and that the decision to part ways was a mutual agreement with Busch saying that it was "time for a fresh start," adding: "Coming to a mutual agreement to go our separate ways is a positive step for me. Over the Thanksgiving holiday I took time to reflect on what is most important to me and realized I need to find a way to put the fun back into racing.

"I am grateful to Penske Racing for six very productive years," he continued. "Together we won a lot of races - 16 in all. Leaving a great organization and a lucrative contract is not easy, but it's an important step for me and allows me to take a deep breath to work on things that can make me a better driver and a better person. I want to personally thank Roger Penske for the opportunity that he has given me."

It's unclear whether there are any remaining seat openings for Busch for next year, or whether he intends to take some time out. He revealed last week that he was seeing a sports psychologist about controlling his anger after races, after a series of blow-ups over the year aimed at both his team boss Roger Penske, and his former crew chief Steve Addington who exited Penske himself last week to take over as Tony Stewart's crew chief in 2012.

"I recognize the passion and emotion that have helped me succeed on the track need to be better channelled off the track," Busch said. "The past few months I began working with a sports psychologist to help me better deal with my emotions, especially following moments of frustration during competition.

"I need to be a better person on the radio, to the team, as a leader," he continued. "I need to harness what happens in the race car and keep it there, and then I need to step out of the car and understand that if we didn't reach our goal for that day or that moment, that it's going to be alright at the end."

The 2004 Cup champion added: "I never want to take for granted that it's a privilege to earn a living as a NASCAR driver. As I begin this new chapter in my career, I'm excited about the future and committed to making the changes necessary for me to enjoy racing again, to compete for championships and to better represent NASCAR, my sponsors, my team and my fans."

Busch had denied as recently as Thursday that he was at any risk of losing his race seat over recent events, but the #22's primary sponsor Shell/Pennzoil was notably unhappy with events at Homestead-Miami and may have played an important role in today's development.

A statement from the company said that "we support the mutual agreement by Penske Racing and Kurt Busch to end their driver/race team relationship, effective immediately," and stressed that its motorsports sponsorship was intended to raise awareness "for our products and brands and to promote them to consumers in a positive way." The company said that they intended to remain with Penske in light of today's news.

Busch has been with Penske Racing since 2006, after five years at Roush Racing. Busch started off the 2011 season on a high with victories in the Budweiser Shootout and Gatorade Duel curtain-raiser non-championship events at Daytona, and won two Cup races during the remainder of the year on his way to making it into the Chase, although his form slumped on the post-season shootout and he ended up in 11th place.

"We won at Sonoma. We won a Chase race at Dover. We were nine points out of the lead three races into the Chase. That's the season that I think of. I don't think of those last three races," he said.

SPEED cable TV channel analyst and former NASCAR driver Jimmy Spencer suggested that this could be the end of Kurt Busch's career at the top level of US motorsport. "My gut feeling is that he can't truly come back from this. He won races this year, made the Chase and is a former champion, and yet he still was let go. That does not bode well for his future.

"Kurt is a hell of a driver and a past champion but he thinks he's above everyone and everything. You can't treat people the way has - I don't care who they are. Kurt has disgraced NASCAR and his sponsors," he continued, adding: "In my opinion, Roger Penske is the most honourable man in motorsports and he has the utmost respect of everyone in NASCAR and IndyCar. But Busch has treated him with the most disrespect I've ever seen a driver treat an owner."

"I think the message this sends is that just because you win races, you can't be a horse's rear-end," said another former driver, Kyle Petty. "This sends a huge message to young and up-and-coming drivers that just because you're cocky and arrogant and think you're the greatest, you still have to fit into the boundaries and the mould."