Matthew Simmons, who rattled the energy industry by arguing the world was rapidly approaching peak oil production capacity, died at his home in North Haven, Maine, the energy research group he founded said on Monday.
He died suddenly on Sunday, his Ocean Energy Institute said in a statement.
Simmons, 67, a former adviser to U.S. President George W. Bush, had a heart attack while in a hot tub, local media reported, citing a report by the Knox County Sheriff's Office.
In his 2005 book "Twilight in the Desert," Simmons argued Saudi Arabia's oil reserves were nearing the highest levels of production they were capable of achieving, after which point the world's yearly oil supply would begin to decline.
While Simmons' views on peak oil were regarded as somewhat controversial, he drew even more attention for a June 9 interview with Fortune magazine, in which he predicted BP Plc<BP.N> would be driven bankrupt in "about a month" as the cleanup costs for the Gulf of Mexico oil spill mounted.
A week later, Simmons & Co International (SCI), the investment bank that Simmons founded in 1974, said it was cutting ties with its founder, who until that point had served as chairman emeritus.
Simmons said he was retiring from SCI to devote his time to The Ocean Energy Institute, a think tank and venture capital fund addressing the challenges of U.S. offshore renewable energy.
"Matt Simmons was an innovative thinker who pushed ideas that have the potential to yield a more environmentally and economically sustainable future for Maine and the world," Maine Governor John Baldacci said in a statement.
"Our state has been viewed as a leader in alternative energy in part because of the groundbreaking work spearheaded by Matt Simmons and the Ocean Energy Institute," Baldacci said.
(Reporting by Scott Malone and Edward McAllister; Editing by Daniel Trotta and Eric Beech)