An oil tycoon sold his company for $26 billion this year — but died before the deal closed

• Autry Stephens agreed to sell his company for $26 billion in cash and stock in February.
• The oil tycoon was set to become one of the world's 100 richest people, but he died this month.
• Stephens wasn't fussed about lavish living, and his family will still profit if the deal closes.

Autry Stephens struck a deal in February that would have made him America's richest oilman and one of the world's 100 wealthiest people — but died before it closed.

The founder and owner of Endeavor Energy Resources agreed to sell the Texas oil producer to Diamondback Energy for $26 billion this spring. A cancer diagnosis spurred his decision to cash out, he told The Wall Street Journal at the time. Stephens was 86 when he died last week.

The planned merger, still expected to close in the fourth quarter, has added $17.5 billion to Stephens' net worth this year, per the Bloomberg Billionaires Index . The late entrepreneur's fortune nearly quadrupled since January from about $6 billion to $23.4 billion, placing him 85th on the list.

Only 14 people on Bloomberg's rich list have made more money this year, and none of them rank lower than 18th. Stephens has even outpaced the world's richest person, Elon Musk (up $15.1 billion), as well as the likes of former Microsoft CEO Steve Ballmer (up $16.3 billion), and Asia's richest individual, Mukesh Ambani (up $16.4 billion).

Stephens' immediate family members are the sole owners of Endeavor following his demise, per Bloomberg. They're poised to receive the $8 billion in cash and 117.3 million Diamondback shares from the deal in his stead. The stake was worth about $17 billion just before the tie-up was announced and is now valued at $22 billion due to Diamondback's rising stock price.

Stephens may have decided that given his ill health and the lack of an obvious heir to take over the family business, it was best to secure his family's future.

The oil tycoon was still a multi-billionaire when he died, but he appears to have shared investor Warren Buffett's taste for a simple life .

Stephens grew up on a peanut and watermelon farm, drove a beaten-up Toyota Land Cruiser, and eschewed private jets for cheap flights with Southwest Airlines, the Journal reported.