Abstract Thermodynamic calculations indicate that, at diagenetic temperatures, laumontite is stable only in the presence of fluids of high pH and low . This is supported by experimental dissolution studies that suggest that laumontite is soluble in the presence of carboxylic acids. As both CO 2and carboxylic acids are produced prior to and during hydrocarbon generation, laumontite is unlikely to form in sandstones plumbed to source rocks during the maturation process. It is more likely that early formed laumontite cements will be destroyed and secondary porosity created by the processes associated with maturing kerogen. Thus potential reservoir rocks may be found in or below laumontite-bearing sandstones. Laumontite in hydrocarbon environments would most likely have formed late relative to hydrocarbon maturation. The sedimentary basins of California may demonstrate such a late-stage, hydrothermal origin for laumontite. The concept of laumontite as an economic basement for hydrocarbon exploration must be carefully evaluated on a case-by-case basis.