 He died during a trip to France due to an arterial hemorrhage possibly caused by overwork.Daniel O’Day, Sr. was the close personal friend of John D. Rockefeller; he was said to be the master mind on the transportation end of the Standard’s scheme for monopolizing the oil business of the country at a time when the opposition of the independent petroleum companies was at its height.O'Day, Sr. had retired from active participation in Standard Oil’s affairs during 1905; his place in the business was largely taken by his son, Daniel O’Day, Jr., who was specially trained to succeed him.