Paleomagnetic orientation of natural fractures in cores from fractured reservoirs is one of the paleomagnetic services provided by Applied Paleomagnetics to the petroleum and geotechnical industries worldwide since 1986. Our paleomagnetic fracture orientation service is used around the world in cores from carbonate and clastic naturally fractured oil and gas reservoirs to determine fracture permeability anisotropy. Our paleomagnetic fracture orientation service is integrated into our paleomagnetic core orientation service, which we first developed in 1982. Fracture studies using paleomagnetically oriented cores have better resolution than image logs, allowing better determination of natural fracture density, fracture trends, and fracture apertures. Natural fractures in cores oriented with respect to a known straight line (the Master Orientation Line marked on the core during paleomagnetic core orientation) are more accurately oriented than if measured with respect to a rotating scribe line (as with electronic multishot). In our paleomagnetic fracture orientation service, we measure natural fracture density, natural fracture apertures, natural fracture trends, and the angle between induced and natural fractures. We also paleomagnetically orient fractures induced during coring. Induced fractures are parallel to in situ stress and can be used to predict the orientation of hydraulic fractures created for reservoir stimulation. Natural fractures striking parallel to in situ stress are more likely to be open and to remain open during production of hydrocarbons. Case History 1, from a fractured sandstone reservoir in which cores were oriented using our paleomagnetic fracture orientation service, shows four sets of natural fractures with different orientations relative to in situ stress as defined by induced fractures. Natural fracture Sets 1 and 3 are most open, have widest apertures, and strike <45° from in situ stress. Natural fracture Sets 2 and 4, which are nearly closed, strike >45° from in situ stress. Case History 2, from a fractured carbonate reservoir in which cores were oriented using our paleomagnetic fracture orientation service, shows that Set 1 natural fractures striking <30° from in situ stress are most open, whereas Set 2 natural fractures which are perpendicular to in situ stress are all healed.