Utilize the input text as a context reference, choose the right relationship between 'Tullow Oil' and 'Petroleum' from the options.
Options: director/manager, product/material produced, stock exchange, owned by

Tullow Oil (LSE: TLW.L - news ) , Chevron (Swiss: CVX.SW - news ) , Anadarko and African Petroleum had been among companies carrying out exploration in Liberian waters.
product/material produced