Hanna IV, the fourth in a series of underground coal gasification experiments fielded and conducted by the Laramie Energy Technology Center, was originally designed as a three-well linear module. A major process objective was to confirm the ability to relay the reverse combustion linking and forward gasification techniques from one pair of process wells forced an extended interruption of the experiment and precluded the relaying of the process as originally conceived. The initial phase of Hanna IV is referred to as Hanna Iva; the continuation of the experiment is referred to as Hanna IVb.