In the present study we performed an experimental investigation of the Rayleigh–Taylor instability (RTI) in a mixing zone between two gases entrapped into accelerated motion by a nonstationary compression wave. Acceleration g was ∼1.5·107 cm/s2, Atwood numbers ranged from 0.04 to 0.77. A mixing zone was formed by an oxygen-hydrogen mixture and an inert gas (Ne, Ar, Kr, Xe) or SF6. The initial gas pressure was 0.5 atm. A specific feature of our experiment is compressibility of media tested and initially continuous interface between gases of different densities. The present work is a continuation of investigations on nonlinear, transition, and early turbulent stages of the RTI.