Passive acoustic monitoring (PAM) has emerged as a highly efficient technology to conduct long-term monitoring of marine mammals at species dependent, local to basin scales, providing valuable new insights into species distributions and migration patterns. To study Antarctic mammals, we deployed up to ten moored, autonomous acoustic recorders in the Atlantic sector of the Southern Ocean. Due to this region’s remoteness, challenging accessibility, and ensuing logistic constraints, especially during winter, recording devices were/are deployed for two years or longer, resulting in high demands on their power efficiency and storage capability. Two types of recorders, AURAL and MARU, which were deployed in March 2008 and December 2008, respectively, were recovered in December 2010. More recently, a set of eight, newly developed recorders (SONOVAULT), were deployed in December 2010, and are scheduled for recovery in December 2012. While in-situ recordings are hence available for AURAL and MARU, for SONOVAULTs extensive laboratory tests have been performed. Based on these recordings, this paper provides a user-based comparison of these three types of acoustic recorders, discussing their technical specifications and limitations (including recent enhancements) along with their actual performance and data quality. The paper concludes with a discussion of future needs for long-term monitoring applications along with each instrument’s potential to meet such requirements.