DUBAI - Qatar's Commercial Bank said on Thursday it has made an offer to buy an additional stake of 15.2% stake in National Bank of Oman for 49.4 million rials ($128 million).

The deal will boost Commercial Bank's stake in the Omani lender to over 50%, keeping it as the biggest shareholder ahead of the government of Oman's 26.18% stake, according to Refinitiv data.

The news send shares of National Bank of Oman up 9.5% in early trade.

Banks generally try to keep a majority stake in a rival lender because a minority stake is seen as punitive for capital under Basel III, the global framework for capital adequacy. ($1 = 0.3850 Omani rials)

(Reporting by Saeed Azhar; editing by Jason Neely) ((Saeed.Azhar@thomsonreuters.com; +971 44536787; Reuters Messaging: saeed.azhar.reuters.com@reuters.net))