The results of geological, petrographical, geochemical and mineralogical studies, performed to determine the coal-forming paleo-environmental conditions which gave rise to anomalous enrichments in organic sulphur, molybdenum and uranium in the Oligocene Mequinenza subbituminous coal deposit of northeastern Spain, are summarized. This paper demonstrates the major influence exerted by the paleohydrology of the depositional framework on the early diagenetic evolution of the precursor peat deposits. The S, Mo and U enrichments, the preservation of aragonite and chlorophillinite, and the high degree of gelification of the Mequinenza coal are a consequence of alkaline syngenetic conditions in the depositional environment. Similar conditions can be inferred for many Mesozoic and Tertiary coal deposits in the Mediterranean region (Mallorca, Sardinia, Hungary, Bulgaria, Serbia, Greece and Turkey). However, the source of sulphur may have been different and have included Triassic and Early Jurassic sulphate recycling scenarios or volcanic sources, Whatever the source, sulphur enrichment is always influenced by the alkaline depositional environments developed in basins generated during the Alpine Cycle in circum-Mediterranean mobile belts.