1984, file photo, T. Boone Pickens, of Mesa Petroleum, speaks at the Helmsley Palace Hotel in New York.
1984, file photo, T. Boone Pickens, of Mesa Petroleum, speaks at the Helmsley Palace Hotel in New York. AP Photo - David Pickoff

Oil tycoon T. Boone Pickens dies at age 91

T. Boone Pickens, a brash and quotable oil tycoon who grew even wealthier through corporate takeover attempts, has died. He was 91.

Pickens was surrounded by friends and family when he died of natural causes under hospice care at his Dallas home, spokesman Jay Rosser said on Wednesday.

Pickens suffered a series of strokes in 2017 and was hospitalised that July after what he called a "Texas-sized fall".

An only child who grew up in a small railway town in Oklahoma, Pickens followed his father into the oil and gas business. After just three years, he formed his own company and built a reputation as a maverick, unafraid to compete against oil-industry giants.

In the 1980s, Pickens switched from drilling for oil to plumbing for riches on Wall Street. He led bids to take over big oil companies including Gulf, Phillips and Unocal, castigating their executives as looking out only for themselves while ignoring the shareholders.

Even when Pickens and other so-called corporate raiders failed to gain control of their targets, they scored huge payoffs by selling their shares back to the company and dropping their hostile takeover bids.

Later in his career, Pickens championed renewable energy including wind power. He argued that the United States needed to reduce its dependence on foreign oil.

He sought out politicians to support his "Pickens Plan", which envisioned an armada of wind turbines across the middle of the country that could generate enough power to free up natural gas for use in vehicles.

"I've been an oilman all my life, but this is one emergency we can't drill our way out of," he said in 2009.

Pickens' advocacy for renewable energy led to some unusual alliances. He had donated to many Republican candidates since the '80s, and in the 2004 presidential campaign he helped bankroll television ads by a group called Swift Boat Veterans for Truth that attacked Democratic nominee John Kerry. A few years later, Pickens endorsed a Kerry proposal to limit climate change.

Pickens couldn't duplicate his oil riches in renewable energy. In 2009, he scrapped plans for a huge Texas wind farm after running into difficulty getting transmission lines approved, and eventually his renewables business failed.

"It doesn't mean that wind is dead," Pickens said at the time. "It just means we got a little bit too quick off the blocks."

Pickens flirted with marketing water from West Texas, acquiring water rights in the early 2000s in hopes of selling it to thirsty cities. But he couldn't find a buyer, and in 2011 he signed a deal with nearby regional water supplier to sell the water rights beneath 85,400 hectares for $US103 million.

In 2007, Forbes magazine estimated Pickens' net worth at $US3 billion. He eventually slid below $US1 billion and off the magazine's list of wealthiest Americans. In 2016, the magazine put his worth at $US500 million.

Besides his peripatetic business and political interests, Pickens made huge donations to his alma mater, Oklahoma State University - the football stadium bears his name, and he gave $US100 million for endowed faculty positions.

Pickens' foundation gave $US50 million each to the University of Texas' M.D. Anderson Cancer Center in Houston and UT Southwestern Medical Center at Dallas.

He was among those who signed a "giving pledge" started by billionaire investor Warren Buffet and Microsoft co-founder Bill Gates, promising to donate a majority of his wealth to charity.

"I firmly believe one of the reasons I was put on this Earth was to make money and be generous with it," he said on his website.