Matthew Simmons, an international oil expert who most recently focused on developing renewable energy from the waters off Maine, died Sunday night of an apparent heart attack.

He was 67.

Simmons founded the Ocean Energy Institute in 2007, and hosted the grand opening of its new office last month in Rockland.

The think tank and venture capital fund works to attract investment in research to make Maine a global leader in offshore wind and other sources of energy from the ocean.

According to police reports, Simmons suffered a heart attack while he was in a hot tub at his summer home on North Haven.

He had a year-round home in Rockport.

An autopsy is planned for today in Augusta, according to the Knox County Sheriff’s Office.

Simmons was a leading energy investment banker and a former energy adviser to President George W. Bush.

He wrote the 2005 book “Twilight in the Desert: The Coming Saudi Oil Shock and the World Economy,” which laid out an argument that the world was approaching its peak oil production.

Simmons’ death shocked his colleagues at the Ocean Energy Institute.

The organization plans to continue his work, said Bob West, the institute’s managing director.

“That’s our goal, to carry his vision forward,” he said. “Matt wanted it to continue and there’s a process in place.”

Wickham Skinner of Tenants Harbor knew Simmons for 42 years. The two met while Simmons was a student at Harvard Business School.

Skinner said he persuaded Simmons to come to Maine, where he became an active member of the Rockland community. He served on the board of directors for the Island Institute and the Farnsworth Art Museum.

Simmons bought the Strand Theater in Rockland about five years ago and restored it, Skinner said.

On Monday, the theater was closed in his memory.

On its marquee was the message, “Matthew Simmons, A Friend to Rockland.”

Skinner said his friend split his time between his homes in Maine and his home in Houston.

Gov. John E. Baldacci met with Simmons a number of times, and recognized Simmons’ leadership during this year’s State of the State address.

Simmons believed that to meet its future energy needs, society had to look beyond fossil fuels and develop energy by harnessing natural resources in a responsible way.

On Monday, the governor said, “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.”

The Ocean Energy Institute is part of a consortium led by the University of Maine that has received millions of dollars from the federal government to research and develop offshore wind turbines.

Baldacci said, “I visited Matt and his team last month and thanked them for their partnership with the state as we aggressively build an independent energy future for Maine.”

U.S. Rep. Chellie Pingree, D-Maine, who has a home on North Haven, said, “Matt was a neighbor and a friend, and the news of his passing is profoundly sad.

“Matt was a visionary, a man of ideas and an outspoken advocate for the things he believed in. He was dedicated to making Maine a leader in offshore wind energy and made significant contributions to life in the midcoast,” Pingree said.

U.S. Sen. Olympia J. Snowe, R-Maine, called Simmons one of the nation’s most prominent and innovative energy scholars.

“Matt possessed a unique and powerful voice as a leader in the energy industry to reduce our dependence on foreign sources of oil,” Snowe said in a prepared statement.

Simmons was the founder of Houston-based Simmons & Co. International, the largest energy investment company in the world.

Skinner, his former professor, said Simmons gradually retired from the company, and became its honorary chairman about a year ago.

U.S. Sen. Susan Collins, R-Maine, who worked with Simmons on the development of UMaine’s deepwater offshore wind energy initiative, said, “Matt was a pioneer in alternative energy This is truly a tragic loss.”

A statement posted on the Ocean Energy Institute’s website said that Simmons is survived by his wife, Ellen, and their five daughters.

The statement said details of his funeral are pending. Simmons’ family is asking that donations be made to the Ocean Energy Institute.

Staff Writer Dennis Hoey contributed to this report. 

Staff Writer Tux Turkel can be contacted at 791-6462 or at: tturkel@pressherald.com