A brew of state activity, federal inaction, industry interests, and environmental concerns is bubbling over in response to public demands for more information about the chemicals used in hydraulic fracturing. Fueling the debate is the oil and gas industry’s refusal to reveal the identity of the substances in fracking fluids.

Fracking, an unconventional oil and gas recovery method, involves injecting large volumes of fluid deep underground to break up tight rock formations to extract hydrocarbons. Composed of about 90% water, 10% proppant—sand or other particulate matter—and less than 1% assorted chemical additives, the fracking fluid that oil and gas drillers use varies in composition depending on the recovery method and underlying geologic formations.

The concern over the chemicals in this fluid has grown in recent years as fracking has become more popular. The extraction technique has boosted the U.S. production of natural gas by nearly 40% in the past decade. Even as the price of natural gas tumbled in 2014, fracking is expected to continue its growth to account for more than 75% of natural gas production by 2035, according to industry projections.

Fracking’s contributions to job creation and U.S. energy independence have been significant, experts say. The fast-moving industry has blossomed in the Great Plains and in some parts of the Northeast.

As the public’s call for environmental protections and information about what substances are getting injected into the ground has grown louder, some states have created their own rules to force the industry to reveal more information about fracking chemicals. In the absence of federal guidance, however, these disclosure rules have varied in scope and efficacy from state to state.

In 2010, Wyoming became the first state to require disclosure of fracking fluid additives. Since then, some 30 states have adopted rules or are in the process of doing so. But those actions are not enough to satisfy advocates for openness. That’s because with few exceptions, state rules exempt industry from having to publicly disclose chemicals it claims are trade secrets.

These exemptions are, in most states, easily obtained, rendering disclosure rules largely ineffective for informing the public, says Matthew McFeeley, an attorney with the Natural Resources Defense Council, an environmental group. Opting out of disclosure can be as simple as marking a checkbox or writing “trade secret” on a form, he says.