If IIRC the contract Shell awarded to Bristow in 2005 was a 7 year contract with several 1 or 2 year extensions that can be automatically activated. This is arrangement is normal in the industry so that the incumbent has to keep operating until their successor is ready.
Even within those extensions we can decrease the number of aircraft with 90-120 days notice. This really does make it easy to shop around for a good deal.
These days the smaller operators are proving very competitive and far more willing to operate as directed by the customer's highly skilled advisors.