How will this save money?
There are really only two ways that outsourcing can produce genuine savings while providing reasonable profits to the outsourcing supplier:
[1] if there are substantial economies of scale - hardly likely for an outfit the size of BP; or
[2] if the existing setup is already FUBAR - in which case fire the dolts* responsible and employ someone who knows what they're doing.
Of course the beancounters and suits are only worried about the next quarter's numbers (maybe next year's, if you're lucky enough to have really 'far-sighted' management) and like the swift cash injection from the 'sale and leaseback' part of the outsourcing agreement.
* And if you can't manage your own internal IT operations, what the hell makes you think you can manage outsourced IT operations. And if you think that outsourced operations don't require careful and attentive management, you're setting yourself up for an absolutely epic fail.