Transformation and distribution of sulfur compounds in fossil fuel thermal processing depends on the bonding forms of sulfur in the specific feed-stock, thermal processing conditions and the technology used. This paper is focused on oil shale semicoking in a pilot-scale solid heat carrier retort (Galoter process) where oil shale is heated by means of mixing with ash from retorted shale combustion. The effect of out-burning conditions of the solid semicoking residue in the technological regeneration furnace on transformation and distribution of sulfur in retorting products is shown for two types of Estonian oil shales - dictyonema argillite and kukersite oil shale. These oil shales used differ significantly in their sulfur composition (total sulfur and sulfur bonding forms present) and mineral matter content.