The 302,700 workers estimated to work for services and exploration and production companies marked the first time employment in the industry has exceeded 300,000 since the index began tracking the numbers in 1995, its developer, economist Karr Ingham, said.

"What's driving this is the massive expansion in the Permian and the creation of activity and rapid expansion in the Eagle Ford," Ingham said.

"But in virtually every corner of the state there is active production. There has been a new record with every passing month since June 2011," he said of the employment figure.

Industry employment in July grew at a year-over-year rate of 7 percent, with upstream payroll adding more than 20,000 jobs in the last 12 months.

Ingham prepares the index for the Texas Alliance of Energy Producers, a trade group of independent producers. He uses statistical methods based on Texas Workforce Commission estimates.

Read more