The liberation of hydrogen sulfide (H2S), molecular hydrogen (H-2) and hydrocarbon gases as well as CO2 from three immature carbonaceous rocks has been studied by Micro-Scale Sealed Vessel (MSSV) pyrolysis in the temperature range from 350 to 600 degrees C at a heating rate of 1 degrees C/min. The samples analyzed were the lacustrine Miocene Condor Shale from Australia (CON-1) and two marine marlstones (HBY-1 and HBY-2) from Southern Lebanon, with different contents of total sulfur (TS; 0.38-1.6%), total organic carbon (TOC; 3.7-11.6%) and total inorganic carbon (TIC; 2.8-9.3%). The Condor Shale has a high siderite (FeCO3) content (20.3%) and 0.2% pyrite (FeS2). The total iron (Fe) content is 10.5% and the kerogen is sulfur-lean. The iron (Fe) contents of the HBY samples are below 1% (0.9% and 0.3%, respectively) and insignificant amounts of pyrite are present, indicating a predominance of organic sulfur (sulfur-rich kerogen) with S-org values of > 1%. The low Rock-Eval T-max values support the presence of sulfur-rich, labile kerogen. CO2 was the major pyrolysis gas released from the CON-1 over the entire pyrolysis temperature range while no H2S was detected at any temperature level. The molar H-2 yields tend to exceed the CH4 yields up to 475 degrees C while at higher pyrolysis temperatures CH4 is the predominant hydrogen-containing product gas. For the HBY-1 and HBY-2 samples H2S and CO2 are the major product gases up to 450 degrees C. Up to this temperature H2S is also the predominant hydrogen-bearing gas component. Subsequently methane and ethane yields exceed the molar H2S yields. At higher temperatures an increasing proportion of hydrogen is released as H-2. Ultimately the molar H-2 yields approach or even exceed the H2S yields from the sulfur-rich HBY samples. At pyrolysis temperatures < 450 degrees C the sulfur-rich kerogens liberate more hydrogen as H2S than as CH4 and H2. At high temperatures hydrogen release as H-2 and H2S is less significant. These results indicate that, besides the amounts of molecular hydrogen released, the liberation of H2S should be taken into account for a comprehensive H mass balance of organic sulfur-rich source rocks. Approximately 50% of the hydrogen in sulfur-rich kerogen is released as CH4 during cracking at high temperatures (600 degrees C).