If, however, A must give notice for a substantial period of time before ending his liability under the contract, and such liability is to last until the end of time for which the notice is given, A's promise is a consideration. Thus if A has a right to end the contract at the end of any year,1 or on ten days' notice,2 or on two weeks' notice,3 A's promise is a consideration. So a contract by which A is to drill a well for B at so much per foot, according to depth, A to drill until water is struck or B orders drilling stopped, is supported by consideration.4