The law recognizes trespass liability for subsurface intrusions, at least in some circumstances. Further, courts sometimes have stated that ownership of land extends to the earth's center. But such statements are dicta. Few courts have carefully considered the maximum extent of subsurface ownership or subsurface trespass liability. Courts in two jurisdictions have recently addressed whether a person incurs liability when he causes hydraulic fracturing fluid to intrude into the subsurface of a neighbor's land, but the courts reached opposite conclusions, with each suggesting that public policy supported its position. Neither adequately examined the legal issues. Careful consideration of trespass concepts demonstrates that a person should not incur liability for such intrusions unless he designed the fractures to extend beneath the neighbor's land or the fractures extended further beneath the neighbor's subsurface than the maximum typical discrepancy between planned and actual fracture lengths. Further, this result serves the public policy concerns addressed by each court that recently addressed this issue.