In the context of the input sentence, determine the relationship between 'Tullow Oil' and 'Petroleum'.
Options: creator, member of, owner of, product/material produced

Wed, Jul 15, 2015, 11:40 BST - UK Markets close in 4 hrs 50 mins When Will It Be Time To Buy Explorers Gulf Keystone Petroleum Limited, Enquest Plc And Tullow Oil plc?
product/material produced