English English Wikipedia has an article on:underbalanced drillingWikipedia Etymology From under- + balanced. Pronunciation Audio (US):(file) Adjective underbalanced (not comparable) Describing a method of drilling for petroleum in which the pressure in the wellbore is kept lower than that of the formation being drilled, thus allowing fluid to enter the well as soon as it is found. See also overbalancedRemove adsWikiwand - on Seamless Wikipedia browsing. On steroids.Remove ads