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In the Khatatba sandstones (Middle Jurassic, Salam oil field, Egypt), detailed fluid inclusion analyses in the quartz overgrowths reveal a complex history. The earliest cement zones precipitated from hot, connate freshwater and seawater (Th = 133-162 degrees C; salinity = 0-3.5 wt.% NaCl eq.). A second phase of quartz precipitated from brines of variable salinities (Th = 125-148 degrees C; salinity = 5-20-wt.% NaCl eq.), inconsistent with connate fluids. Both phases of quartz cementation resulted from multiple events of injection of hot fluids related to fracturing, quartz precipitation being caused by cooling after injection. The final phase of quartz precipitated from consistently high salinity brine (Th = 114-133 degrees C; salinity = 21-24 wt.% NaCl eq.) associated with oil (Th = 79-127 degrees C) during a period of overall cooling. (C) 2000 Elsevier Science B.V. All rights reserved.