Complex sentence: Prior to this he served as Leader of the PetroScience Group at Geotechnical Resources, Ltd, Calgary, Alberta, and before that held technical positions with ESI Resources, Ltd, Calgary, and Earth Sciences Inc., Golden, Colorado.
Split into simpler sentences: Prior to this he served as Leader of the PetroScience Group at Geotechnical Resources, Ltd, Calgary, Alberta. Before that he held technical positions with ESI Resources, Ltd, Calgary, and Earth Sciences Inc., Golden, Colorado.