Tata Consultancy Services on Wednesday bought Citigroup’s Indian business processing outsourcing unit for $505m in a deal that could become the first of many as global financial services groups seek to raise capital to weather the credit crisis.

As part of the deal, Citigroup has agreed to guarantee it will source $2.5bn of services over more than nine years from the unit, Citigroup Global Services, making the US firm TCS’ largest client with around $500m of business a year including other contracts.