I saw Heart of the Sea and was thinking that even in the turn of the century petroleum oil industry would not be a huge treat to whaling. (Since much of whaling continued till the 1970s) but did those in the whaling industry get involved with petroleum oil industry at all
In The Prize by Yergin we learn that the primary market for whale fat was lamp oil. Petroleums chief use ca 1870 was for kerosene, a superior alternative to whale oil. Standards Oil developed a near monopoly in the US kerosene market.
I don't believe the book mentions any significant whaling interest establishing a toehold in kerosene; certainly Rockefellers chief competition and target for takeover was other oil men.
The continued interest in 20th century whaling was certainly not for lamp oil.