[en] The reversed field pinch magnetic equilibrium in the high aspect ratio (R/a approximately equal to 8.8) Extrap T1 experiment has been studied using an insertable magnetic probe. High current density plasmas, about 14 MA/m² on axis, with reversal ratio and pinch parameter of F approximately equal to -0.5 and Θ approximately equal to 1.8 are considered. The experimental μ-configuration is found to be flat from the central region out to 0.6a, approaching zero at the wall. The pressure profile flat in the central region, with the steepest gradient between 0.6a and 0.8a. Values of βθ = 0.16 and <β> 0.07 are found. Linear stability calculations show that the measured equilibrium, given a conducting wall at the plasma boundary, is stable with respect to all current driven ideal and resistive MHD modes. However, m=1 tearing modes resonant inside the reversal surface are close to marginal stability. When the conductivity of the linear is disregarded and an 18% vacuum region is included in the stability calculations, the m = 0 and the externally resonant m =1 tearing modes become unstable. The configuration is found stable with respect to ideal interchange modes. The resistive interchange stability is also briefly discussed