Update: On September 10, the Texas Railroad Commission concluded that these small earthquakes that occurred near Azle, Texas likely were not caused by drilling operations conducted by EnerVest Operating LLC. The Texas Railroad Commission has concluded that small earthquakes that occurred near Azle, Texas, from late 2013 through spring 2014 likely were not caused by drilling operations conducted by XTO Energy Inc., an Exxon Mobil Corp. subsidiary. The Railroad Commission regulates the exploration and production of oil and natural gas in Texas.