Investment banker in the oil and energy field who was a prominent proponent of the peak oil theory.
He was shocked by the 1973 energy crisis when the Arab states instituted an oil embargo. He founded his own investment firm Simmons & Company International.
His influential 2005 book argued that oil production from Saudi Arabia was peaking and would begin to decline.
He had five daughters with his wife Ellen.
He was hardly the first to claim that oil production would soon peak. Maron Hubbert made the same prediction in 1956 about the year 1970.