April 2015 was a watershed month for natural gas producers. Marcellus Shale gas wells in Butler County are a big part of the reason why.

For the first time ever, natural gas surpassed coal as the fuel of choice for electric power generation in the United States.

Federal data shows gas-fired plants around the country produced 92,516 gigawatt hours (GWh) of electricity in April, compared with 88,835 GWh produced with coal, according to the federal Energy Information Administration, an independent branch of the U.S. Department of Energy.

That represents a market share of about 31.5 percent gas and 30.2 percent for coal. The other 38 percent of U.S. electricity comes from nuclear, solar, wind and hydroelectric generation.

Just 10 years ago in 2006, coal accounted for nearly half — 49 percent — of all U.S. electric production.

It can’t be overlooked that the Environmental Protection Agency under the Obama administration continues to apply pressure on coal-powered plants to shut down or convert to gas. The EPA’s objective is to reduce atmospheric emissions of carbon dioxide and other greenhouse gases, which are widely believed to accelerate global warming and climate change.

Coal is clearly the culprit. In 2006, when 49 percent of the U.S. electricity production was coal powered, those power plants were responsible for 83 percent of CO2 emissions from electricity generation.

Moreover, gas-generated power plant operators don’t have to dispose of tons of coal ash — another environmental hazard. And while gas drilling has its share of opponents, gas wells are far less disruptive and less intrusive than coal mining and transport.

But the bigger factor is Marcellus Shale gas. Improved techniques for drilling and fracturing, or fracking, the gas-bearing rock formations have resulted in an abundant, affordable new energy source that’s easier to transport and cleaner to burn than coal.

Gas industry analysts say the drilling and processing of Marcellus wells is becoming more efficient, too, meaning the cost continues to fall. That might be bad news for Saudi Arabia and other petroleum exporters. They’ve clung to a strategy of continued full-scale production, hoping that a glutted market and lower prices will crimp Marcellus producers’ margin of profitability.

Indeed, there has been some recent scaling back of Marcellus production. But the industry appears to be firmly rooted and here to stay, heavily invested in wells, pipelines and processing plants throughout southwestern Pennsylvania.

And the Marcellus share of electric generation is projected to continue growing as coal plants continue to diminish.

Coal and gas might change ranks for the next few months or even years. Coal might regain its No. 1 status during peak electric hours in the summer, only to lose it again in the fall as net electric use declines.

But the trend is clear: Gas is gaining on coal.

But there’s another chapter: Renewable energy, although a much smaller factor than coal or gas, is growing at an even faster rate. Wind, solar, hydro and other sources might rival gas one day for preferred electric production — particularly if the correct balance of regulatory and market sources is in place to enhance the incentive for their growth.