Calculated maximum discharges for the largest outflow channel system on Mars, Kasei Valles, based on elevation data from the Mars Orbiter Laser Altimeter (MOLA), are 2 to 4 orders of magnitude lower (8¿104--2¿107 m3 s-1) than estimated previously. Mars Orbiter Camera (MOC) images show morphological evidence consistent with these relatively modest flow rates. Topographic profiles of the outflow channels reveal previously unrecognized narrow, inner channels. Development of a sapping channel network between flow events suggests the system was active over a significant period of time and likely involved several separate flood events. The longer formation history and lower discharge rates may require a long fill time (>25 years) and a warmer climate to form a martian ocean. ¿ 2000 American Geophysical Union