The petroleum oil industry didn't save the whales from extinction as the majority of the worlds whale species were already on the brink of extinction by the turn of the 20th century. The petroluem oil industry had been established for 50 years before this near extinction point. Whaling just became economically non viable simply because the whale fisheries had been fished out. Whaling continued throughout the 1st half of the 20th century and expanded considerably after the 2nd world war after the whale population began to recover.

What saved the worlds whale species was international agreements not to continue exploiting the worlds fishery through pressure from environmentalists during the 1960s and early 1970's. The petroluem industry had now been established for over 100 years. The worlds whale fisheries again collapsed during the 1970s.