McLEANSBORO, Ill. — Across several southern Illinois counties, there's a land rush emerging. And it's the potential of once-inaccessible, underground oil and natural gas that's fueling it.

Out-of-staters recently have converged on Hamilton, Saline and Wayne County to scour through property records and establish who owns underground mineral rights their clients or companies may be able to lease for drilling.

The research by those "land men" is linked to a drilling technique called hydraulic fracturing. That so-called "fracking" involves blasting water, sand and chemicals into shale to free trapped energy sources.

Critics believe the chemicals have polluted drinking water supplies. The industry says there's no proof.

The intense interest stems from a belief that the region's shale has oil and liquid hydrocarbons that are rarer — and more profitable — than natural gas.