The Eagle Ford Shale is a geological formation directly beneath the Austin Chalk Shale. It is considered to be the “source rock”, or the original source of hydrocarbons that are contained in the Austin Chalk and the Edwards formation above it. The Eagle Ford Shale is found at depths between 4,000 and 12,000 feet. The shale is up to 250 feet thick in some places, generally without natural fracturing present. Most of the production occurs at the convergence of the Stuart City Reef trend and the Sligo Reef Trend.