ABSTRACT: Laboratory drilling experiments were conducted to determine the effects of different test variables on the development of fracture-like breakouts in high porosity Berea sandstone. Tests showed that breakout length is directly proportional to the horizontal principal far-field stress differential, suggesting a potential use of this correlation to estimate in situ stress magnitudes. Larger boreholes produced increasingly longer breakouts, from which we infer that breakouts could reach lengths of several meters in typical oil-field wellbores. Within the ranges tested, neither drill-bit penetration rate, nor drilling-fluid flowrate, had a discernable effect on breakout dimensions or shape. One consistent characteristic of fracture-like breakouts, regardless of testing conditions, was their near-constant width, which averaged 3.3±0.3 mm in all tests. Long breakouts, expected to develop in regions of high differential stresses in rock having similar characteristics to Berea sandstone, may be a potential source of sand production.