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.
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