Take context from the input text and decide on the accurate relationship between 'Tullow Oil' and 'Petroleum' from the options provided.
Options: stock exchange, director/manager, product/material produced, 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