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A borehole breakout forms when the concentrated compressive stress around a drilled hole fractures and removes part of its wall. Opposed damaged sectors widen the originally circular hole. A borehole televiewer images the wall so that the enlargement and its orientation can be distinguished from an isolated natural fracture.

For an approximately vertical hole aligned with a principal stress direction, the long axis of the breakout follows the minimum horizontal compressive stress direction. The strongest tangential compression occurs there even though the distant horizontal compression in that direction is smaller. Inclined holes, pore pressure, drilling pressure and rock strength require a fuller model before orientations or magnitudes are inferred.^[ref]

Mark D. Zoback coauthored research using borehole breakouts to infer in-situ crustal stress. The orientation and shape of borehole-wall failure become informative through a mechanical model relating local stress concentration to the far-field stress.^[ref]