CASPER, Wyo. (AP) — A judge heard arguments Tuesday in a lawsuit that questions state officials' refusal to publicly release the ingredients in hydraulic fracturing chemicals that companies use to drill for oil and gas.

The Powder River Basin Resource Council and others say landowners need to know which chemicals could contaminate their groundwater. The Wyoming Oil and Gas Conservation Commission and companies including Halliburton argue that the ingredients are trade secrets not subject to public release under Wyoming's open records law.

Fracking involves pumping water and sand underground to fracture open oil- and gas-bearing formations. Wyoming was one of the first states to require companies to tell state regulators the ingredients in the chemicals mixed in with that water.

Natrona County District Judge Catherine Wilking said she would rule within two months.

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