The process has led to an energy industry boom.
Mitchell's family, on the family foundation website, said he died of natural causes while surrounded by relatives.
Over his career, he participated in drilling some 10,000 wells, including more than 1,000 wildcats wells drilled away from known fields. His company, Mitchell Energy & Development, was credited with more than 200 oil and 350 natural gas discoveries.
The firm spent nearly two decades developing hydraulic fracturing, finally finding success in North Texas' Barnett Shale formation in the 1990s.
"There's no point in mincing words. Some people thought it was stupid," Dan Steward, a geologist who began working with the Texas natural gas firm Mitchell Energy in 1981 told The Associated Press in an interview last year. Steward estimated in the early years, "probably 90 percent of the people" in the firm didn't believe shale gas would be profitable, and that Mitchell's company didn't even cover the cost of fracking on shale tests until the 36th well was drilled.
But he credited the company namesake as a tenacious visionary.
"There's not a lot of companies that would stay with something this long," he said. "Most companies would have given up."
"Because of Mitchell's persistence ... we are today witnessing an unprecedented boom in domestic energy production and the associated economic benefits in Texas and nationwide," Texas Railroad Commission Chairman Barry Smitherman agreed Friday.
Mitchell sold his energy company in 2002 for $3.1 billion.
According to his biography posted by the Mitchell Foundation, the North Texas gas field that became the foundation of his oil empire was the result of a deal promoted by a Chicago bookmaker.
"His story was quintessentially American," the family statement said. "George P. Mitchell was raised as a child of meager means who, throughout his life, believed in giving back to the community that made his success possible and lending a hand to the less fortunate struggling to reach their potential.
"He will be fondly remembered for flying in the face of convention focusing on what could be, with boundless determination many times fighting through waves of skepticism and opposition to achieve his vision."
George Phydias Mitchell and his wife, Cynthia, who died in 2009, had 10 children. Their work together was "dedicated to making the world a more hospitable and sustainable place," their family said.
Mitchell graduated first in his class of 1940 at Texas A&M University with degrees in petrochemical engineering and geology. He helped pay for his school costs by running a tailoring and laundry business in College Station and selling candy and stationery to his fellow student Aggies, then in later years became the school's largest benefactor with donations topping $95 million.
This year, the annual Forbes list of wealthiest Americans ranked him 239th with a net worth of $2 billion.
Mitchell spent four years in the Army Corps of Engineers during World War II. Afterward, he struck out on his own with a brother and a partner as a wildcatter operation.
Over the years, he spent tens of millions rebuilding his hometown of Galveston, resurrecting a long-dormant annual Mardi Gras celebration and singlehandedly providing money helping to restore the city's historic downtown Strand District.
He donated the land for Texas A&M University at Galveston.
"To say he was a great man with foresight and generosity isn't enough," Adm. Robert Smith III, the school's president, said. "His contributions to this university literally made this institution possible."
His Cynthia and George Mitchell Foundation, founded in 1979, has made more than $400 million in gifts.
Former U.S. Sen. Kay Bailey Hutchison and Lt. Gov. David Dewhurst both called Mitchell a true Texas legend.
"George Mitchell was a pioneer in the energy industry and was admired by many around the world for his entrepreneurial spirit," Dewhurst said Friday.
In the early 1970s, Mitchell began developing The Woodlands, a suburban Houston master-planned community designed as a place for mixed-income residential development with jobs and amenities nearby while preserving the East Texas forest and other natural resources that covered the 27,000 acres. He later would call it his most satisfying achievement.
The Woodlands is now home to about 100,000 people and one of the nation's busiest outdoor performing arts and entertainment venues there carries his wife's name, the Cynthia Woods Mitchell Pavilion.
"His ambition and success have transformed our region," Houston Mayor Annise Parker said. "He was a visionary, and showed his love for Houston through his work and hometown pride."
"He had the right mix of vision, optimism and tenacity, and a love for his fellow man," the Mitchell family statement said. "There's no doubt that he helped make this world a better place."
Funeral arrangements were not immediately released.
Associated Press Writer Kevin Begos in Pittsburgh contributed to this story.
Online: Cynthia and George Mitchell Foundation http://cgmf.org/p/family-statement.html