Abstract: Mississippian carbonates of the southern Canadian Foothills host 19 major oil and gas reservoirs and were formed by the juxtaposition of two primary facies assemblages: (I) a shallow, warm-water assemblage characterized by ooid grainstones, calcified algae, peloids and evaporites, and (2) a more widespread cool/deep-water assemblage made up of bioclastic fragments of bryozoans, echinoids, brachiopods and sponge spicules. The carbonates were deposited in a paleo-equatorial setting, on a lemperarure-stratified, high-energy ramp swept by nutrient-rich, cold upwelling waters. Episodic shifts in facies belts driven by changes in relative sea level resulted in long-term cyclic straligraphy. Foothills Mississippian reservoirs are sheet-1 ike al a large scale but are internally complex due to facies changes related to high-frequency alio- and auto-auiocyclic processes. Surface, shallow- and deep-burial diagenesis and tectonic fracturing amplified heterogeneities and resulted in complex reservoir compartmenialization. The degree to which diagenesis affects porosity depends largely on original sediment composition and mineralogy, which in turn is related to position on the Mississippian ramp. Below the thermocline, cool-water sediments were dominated by organisms with calcitic skeletons. Resulting strata lack extensive early vuggy, moldic and framework porosities that typify shallow, warm-water systems and form relatively low porosity (< 12%), low permeability (1-250 md) reservoirs. These include: 1) limestone stratigraphic traps with primary intergranular and shelter porosity in deep-water bryozoan grainstone and roudstone buildups and 2) fractured dolostones and limy dolostones with secondary intercrystalline and moldic porosity in mid- to inner-ramp echinoid/bryozoan tempestites and megaripple shoals. Warm-water sediments above the thermocline were a variable mixture of bioclasts and non-biogenic grains of calcite, dolomite, silica, aragonite and Mg-calcite composition. Associated reservoirs include: 3) stratigraphic traps in micrilizedooid grainstones, 4) fractured silty peritidal dolomites and peloidal grainstones and 5) siliciclastic coastal dune com- Most Foothills Mississippian reservoirs so far discovered occur in mid- to inner-ramp cool-water crinoid/bryozoan facies. Reservoir development is controlled by dolomitization and development of secondary intercrystalline, leached moldic and vuggy porosity. Exploration fairways are defined by trends that intersect optimal depositional and structural sellings. The best producing wells occur at the leading edge of thrust imbricates in areas of enhanced fracture permeability and high matrix porosity. These reservoirs are typical not only of the southern Fooih>Hs belt but also of Mississippian carbonates of the Peace River Embayment, Will iston Basin, Central Montana Trough and Illinois Basin. Distribution of reservoir units is highly patterned and compares favorably to modern analogues described from the south coast of Australia. Understanding details of sediment production, distribution, packaging and diagenesis in analogous Modem and Tertiary cool- and warm-water carbonate systems is invaluable for optimizing exploration and development success. This paper describes Mississippian strata from the Rocky Mountain Foothills in the southwest corner of Alberta, Canada. Samples from outcrops in the Livingstone and High Rock Ranges and subsurface cores from Coleman, Quirk Creek, Turner Valley and Moose Mountain gas fields (Fig. 1) are interpreted in a regional stratigraphic and sedimentologica) framework for the Mississippian established by Bamber et al. (1981), Richards (1989) and Richards et a). (1994). Facies descriptions build upon the excellent and thorough sedimentological analysis of Mundy et al. (1992). In this paper, we document evidence that 1) Mississippian sediments in the southwestern Foothills were deposited under temperature stratified conditions and that 2) the distribution and productivity of hydrocarbon reservoirs, while ultimately determined by tectonic configuration, is equally dependent upon original depositional facies and diagenetic processes.