OASES is a general purpose computer code for modeling seismo-acoustic propagation in horizontally stratified waveguides using wavenumber integration in combination with the Direct Global Matrix solution technique [1,2,3]. It is basically an upgraded version of SAFARI [4]. Compared to SAFARI version 3.0 distributed by SACLANTCEN, OASES provides improved numerical efficiency, and the global matrix mapping has been re-defined to ensure unconditional numerical stability in the few extreme cases where the original SAFARI has proved unstable. OASES is downward compatible with SAFARI, and the preparation of input files follows the guidelines of the SAFARI manual [4]. The SAFARI manual focused on VMS implementation, but this note will assume UNIX to be the operating system. However, the bulk of the code is operating system independent and is easily implementyed under VMS, MS-DOS etc.