Dan Harrison III leased his 100,000 ranch in south Texas to Shell Oil for $1 billion in cash plus royalties on future oil and gas production from the prolific Eagle Ford shale. The 2010 deal appears to be the biggest ever for a family with deep roots in Texas oil. His grandfather, the first Dan Harrison, was a legendary Texas oilman, teaming up with J.S. Abercrombie to discover gushers like the Old Ocean field in Brazoria County. He built up an oil and ranching empire across Texas. Father Dan Jr. ran the ranchland and was a master breeder of quarterhorses.