16Karstification positively and negatively impacts the quality of carbonate reservoirs; for example, 17 dissolution and brecciation can increase porosity and permeability, whereas cavern collapse or 18 cementation driven by post-karstification fluid flow may occlude porosity and reduce permeability. Karst 19 may also pose challenges to drilling due to the unpredictable and highly variable porosity and 20 permeability structure of the rock, and the corresponding difficulty in predicting drilling mud-weight. 21When combined, outcrop, petrographic and geochemical data can constrain the style, distribution and 22 origin of seismic-scale karst, which may provide an improved understanding of carbonate reservoir 23 architecture and allow development of safer drilling programs. However, relatively few studies have 24 utilized seismic reflection data to characterize the regional development of seismic-scale karst features. 25In this study we use time-migrated 2D seismic reflection data to determine the distribution, scale and 26 genesis of karst in a 3 km (9800 ft) thick, Jurassic-Miocene carbonate-dominated succession in the 27 Persian Gulf. We map 43 seismic-scale karst features, which are expressed as vertical pipes columns of 28 2 chaotic reflections capped by downward-deflected depressions that are onlapped by overlying strata. 29The columns are up to 2 km (6500 ft) tall, spanning the Upper Jurassic to Upper Cretaceous succession, 30 and are up to 5.5 km (18,000 ft) in diameter. We interpret these pipes formed in response to hypogene 31 karstification by fluids focused along pre-existing faults, with hypogene-generated depressions 32 enhanced by epigene processes during key intervals of exposure. Our study indicates that seismic 33 reflection data can and should be used in conjunction with petrographic and geochemical techniques to 34 determine the presence of hypogene karst plays, and to help improve the characterization of carbonate 35 reservoirs and associated drilling hazards. 36 37 Introduction 38