 Due to his close relationship with his wife's brother-in-law, William Avery Rockefeller, Jr., he became interested in the affairs of the Standard Oil Company.In 1871, when Standard Oil was incorporated in Ohio, Jennings was one of the original stockholders.Of the initial 10,000 shares, John D. Rockefeller received 2,667; William Rockefeller, Henry Flagler, and Samuel Andrews received 1,333 each; Stephen V. Harkness received 1,334; Jennings received 1,000; and the firm of Rockefeller, Andrews & Flagler received 1,000.