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, his office is reporting. He was 67.

Simmons founded the Ocean Energy Institute in 2007, hosting a grand opening of its new office last month in Rockland. The  goal of the think tank and venture capital fund was to attract investment in research to make Maine a global leader in offshore wind and other ocean energy sources.

According to police reports, Simmons suffered a heart attack while in a hot tub at his home on North Haven. An autopsy is planned for today in Augusta, according to the Knox County Sheriff’s Office.

Simmons was a leading energy investment banker, a former energy adviser to President George W. Bush, and author. 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 peak oil production.

Simmons’ death came as a shock to colleagues at the Ocean Energy Institute, which is preparing a statement for release later today.

The organization plans to continue his work, according to 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.”

Maine officials were expressing their sympathies this morning.

Gov. John E. Baldacci had met with Simmons a number of times. The Ocean Energy Institute is a part of the 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 also recognized Simmons’ leadership during his State of the State address delivered earlier this year.

“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,” 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, also has a home on North Haven.

“Matt was a neighbor and a friend and the news of his passing is profoundly sad,” she said. “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.”