U.S.-based Kosmos Energy said it is in early preliminary discussions to potentially buy Tullow Oil in an all-share transaction that could create an oil producer focused on Africa. “There can be no certainty that any offer will be made, nor as to the terms on which any offer might be made,” Kosmos Energy said, confirming an earlier statement from Tullow Oil that it had been approached for talks by Kosmos. The U.S.-based oil and gas company reserves the right to vary the form and/or mix of the offer consideration and vary the transaction…