Noble Corporation (NE) announced Monday morning that it has entered a definitive merger agreement with FDR Holdings, also known as Frontier. The deal values the joint venture at $2.16 billion. NE expects the deal to close by the end of July, and noted that it will be accretive to cash flow immediately and to earnings in 2011. NE will acquire a fleet of roughly 23 rig years of contracts that generate roughly $3.2 billion in gross contract backlog.

NE CEO David W. Williams sated that, "Frontier is an excellent strategic addition to NE's existing asset, customer and employee base ... This acquisition is a highly complementary extension of our mid- and deepwater presence and positions us for additional growth in new market segments that can provide further opportunities for Noble and our customers."

Republic Airways Holding Inc. (NASDAQ: RJET) is going shopping. Only a day after making an offer for ailing Frontier Airlines (OTC: FRNTQ), it has made a bid to nab Midwest Airlines from private equity firm TPG Capital. The offer consists of $6 million in cash and a note for another $25 million. If the private equity house takes the deal, Republic will get 100% of Midwest's equity and TPG's secured note of $31 million.

The $25 million in debt is convertible to RJET stock at $10 a share, which gives TPG a bit more upside from the transaction. The seller would also have the right to nominate a member of the buyer's board of directors.

Of course, Republic's CEO, Bryan Bedford, is upbeat about the prospect of buying Midwest Airways, saying it will "enhance the strategic positioning" of his company. Like the proposed acquisition of Frontier, Midwest would continue to operate under its own name, though the target's Boeing 717s would be replaced with Embraer 190s.

MOST NOTEWORTHY: GlobalSantaFe Corp, Transocean, Frontier Oil, Tesoro and Audio Codes were today's noteworthy upgrades:

• JP Morgan upgraded shares of GlobalSantaFe Corporation (NYSE: GSF) and Transocean Inc (NYSE: RIG) to Neutral from Underweight based on valuation and improving deepwater rig fundamentals.
  
• Frontier Oil Corporation (NYSE: FTO) was upgraded at Banc of America to Buy from Neutral as they believe the company's assets are ideally located to access cheap Canadian oil sands production. They feel the stock should trade closer to its replacement value, which they estimate at $55/share.
  
• The firm also raised Tesora Corporation (NYSE: TSO) to Buy from Neutral, as the firm believes Terero is the best play on the extended refining cycle given its exposure to California.
  
• CIBC upgraded shares of AudioCodes (NASDAQ: AUDC) to Sector Outperformer from Sector Performer on valuation after their checks suggested the company's business is stabilizing and cost cutting is tracking ahead of plan, which could bring upside EPS estimates.

OTHER UPGRADES:

• GSI Commerce (NASDAQ: GSIC) was upgraded to Buy from Hold at Jefferies.
  
• Apache Corporation (NYSE: APA) was upgraded to Buy from Neutral at Goldman Sachs.
  
• Amgen Inc (NASDAQ: AMGN) was upgraded to Buy from Neutral at Merrill Lynch.
  
• BB&T Capital upgraded shares of Skechers USA (NYSE: SKX) to Buy from Hold.
  
• Bernstein upgraded shares of Cognizant Technology (NASDAQ: CTSH) to Outperform from Market Perform.