Pennsylvania went from 10th-largest state in oil and natural gas employment in 2007 to sixth in 2012. The employment increase - 259.3 percent, the study said - was the second-largest, after Texas, which added 64,515 jobs.

Since the Marcellus Shale boom began in 2008, there has been debate about the impact on Pennsylvania's economy.

The liberal-leaning Keystone Research Center said 20,943 direct jobs created from Marcellus Shale make up less than 1 percent of Pennsylvania's economy.

"It is a sober assessment of the job gains accrued in this sector," said Keystone labor economist Mark Price. "It's important for people who got those jobs, especially in the places where there's lots of drilling. It just doesn't add up to enough to lead to a dramatic fall in Pennsylvania's unemployment rate, which is 6.9 percent."

Industry supporters counter that critics of the state's shale gas policies fail to account for the indirect employment benefits - suppliers, vendors, and spending by those who work in the industry.

"We have about 240,000 Pennsylvanians working in industries that are supported directly, or made more secure, by the growth of oil and gas activity in Pennsylvania," said Patrick Henderson, Gov. Corbett's deputy chief of staff and energy adviser.

The jobs are in trucking, parts, supply chain, petroleum engineers, and surveyors, Henderson said, "a variety of different industries that are affected by activity in the oil and gas sector."

(Linda Loyd, "Report sees 15K new Pa. jobs from Marcellus boom," 3/2/14)