NEW YORK ( TheStreet) -- While one of Warren Buffett's greatest strengths is his ability to pick out "sure things," not all of bets he has made throughout his career have paid off. In fact, there are a number of investments the Oracle of Omaha has tried his luck with that have done more harm than good.

His bets on the airline industry, Conoco-Phillips ( COP) ando , and Moody's ( MCO) come to mind when mulling particular Warren Buffett investment blunders. All three investments can be seen as stains on his otherwise stellar career.

U.S. Airways is often highlighted as one of Buffett's most costly slip-ups when, in 1995, the investor was forced to write of 75% of his $385 million investment in the firm.

Despite this staggering loss with U.S. Airways, Buffett has not given up on the airline industry. He currently owns NetJets, a fractional jet sharing program. Like his previous experience, this airline company has resulted in numerous headaches for Buffett.

Hoping to turn the company into a profitable venture, he shook up the company's management in 2009, firing CEO, Rick Santulli and replacing him with rumored Buffett successor, David Sokol. It will be interesting to see if Buffett will eventually shed this company from the Berkshire Hathaway ( BRK.A) portfolio.

Conoco-Phillips is another investment Buffett may wish he could take back. The investor first started buying shares of this oil giant in early 2006. His position was dramatically increased in 2008 when Buffett attempted to take advantage of oil prices which, at the time, were rocketing higher.

Unfortunately, the timing of this bet was terrible. When oil prices returned to earth, shares of COP followed suit, resulting in a several billion dollar hit for Berkshire Hathaway.

Whereas U.S. Airways and Conoco-Phillips are notable mistakes due to their monetary damage to Buffett, the Oracle's investment in Moody's has dealt damage to the investor's reputation.

In the aftermath of this most recent economic crisis, Buffett has been noticeably indecisive in his views towards this troubled ratings agency. While he has expressed his disappointment in the company's actions leading up to the meltdown and has been slowly chipping away at his company's stake in MCO, when he was issued a subpoena to appear in front of the Financial Crisis Inquiry Commission, he offered support for the firm, insisting that while they may have made mistakes, no one foresaw the crisis.

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