Shales constitute more than 75% of the drilled rocks in the search for hydrocarbons and an estimated high 90% of wellbore instability problems are credited to their presence. According to Steiger & Leung (1991), more than 600 Million US dollars are spent annually by the oil industry just to corrent the problems due to instabilities. This work presents a new methodology for running triaxial compression tests in shales under undrained conditions. This methodology allows shorter duration of the tests and it is based upon adaptation of concepts traditionally employed in the soil mechanics field. 12 tests have been carried out in shales obtained from offshore Brazil during this work. The tests were divided into 2 groups based upon the nature of the fluid used in the pore pressure lines. The tests results show that this methodology is very efficient. The shear strength behavior of the shale is described and by using the Mohr-Coulomb criterium, the shear strength parameters are a cohesion of 3,17 MPa and phase equal to 25,3°.