The sheer size of the jumbo financing packages investment banks are potentially underwriting to fund three of the largest corporate mergers and acquisitions in the mining and media sectors could test the resilience of the still-stricken international debt markets, according to bankers.

With news yesterday that Microsoft may raise debt financing to support its $44.6bn (€30.4bn) unsolicited bid for Yahoo, any billion dollar package for the US software giant would come on top of a combined $110bn of loans financing BHP Billiton and Vale’s acquisitions of rivals in the mining sector.