The greatest limitation of the spallation process is its inability to spall (or to consistently spall) many rocks encountered in petroleum drilling and mining operations. The New Mexico institute of Mining and Technology has conducted a series of experiments to investigate the possibility of expanding the use of the spallation process to the penetration of rocks generally considered not to be spallable. The methods used during this work were I) spalling at temperatures below that produced by the stoichiometric burning of fuel oil and air, and 2) spalling by alternately hearing and quenching the rock surfaces. No success was experienced in spalling at the lower temperatures but initial rests showed the alternate heating and chilling system to be successful particularly in penetrating travertine limestone. However, continued testing indicated that, unless the rocks are extremely uniform in composition, spalling will result in highly irregular holes or holes that cannot be directionally controlled.