The Lusi mud volcano in East Java has erupted unabated for almost2 yr, flooding an area of 7 km2 and displacing more than 25,000people. Despite its disastrous impact, the mechanism for triggeringthe Lusi eruption remains highly controversial; two distinctmechanisms have been proposed. One hypothesis suggests thatthe eruption was triggered by the Mw 6.3 earth-quake that struckYogyakarta (250 km from Lusi) two days before the eruption.However, an examination of static and dynamic stress changesand stress transfer mechanisms indicates that the Yogyakartaearthquake was at least an order of magnitude too small to reactivatefaults and open fluid flow pathways under Lusi. An alternatetheory suggests that Lusi was triggered by a blowout followingdrilling problems in the nearby Banjar Panji-1 well. Blowoutsresult from an inability to control pore fluid intakes intothe borehole and typically occur when the drilling window (fracturepressure minus pore pressure) is approximately zero and whenthere is insufficient protective casing of the well bore. Poreand fracture pressure data from Banjar Panji-1 indicate thatthe well had a narrow drilling window of only 0-2.3 MPa.Furthermore, two planned casing points were skipped during drilling,resulting in 1742 m of unprotected borehole. The combinationof hazardously narrow drilling window and long uncased boreholewould have made drilling problems in Banjar Panji-1 difficultto control, placing the well at high risk of blowing out. Furthermore,well-bore pressures following drilling problems in Banjar Panji-1reached magnitudes in excess of the fracture pressure and thuswere sufficient to create fluid flow pathways in the subsurface.Therefore, we suggest that no viable method is known by whichthe Yogyakarta earthquake could have triggered the mudflow andthat a blowout in the Banjar Panji-1 well was the most likelymechanism for triggering the Lusi eruption.