PITTSBURGH (AP) -- It sounds like a free-market success: a natural gas boom created by drilling company innovation, delivering a vast new source of cheap energy without the government subsidies that solar and wind power demand.

But those who helped pioneer the technique known as hydraulic fracturing, or fracking, recall a different path. Research has found that over three decades, the federal government contributed more than $100 million in research to develop fracking, and billions more in tax breaks.

Industry pioneers say their effort shows that the government should back research into future sources of energy. Dan Steward is a geologist who began working with a Texas natural gas firm in 1981. He says the government involvement is necessary because many companies would give up on new technologies that take time to become commercially viable.