Replicate 40Ar/39Ar analyses of sanidine from seven Oligocene (28.2 Ma) rhyolite flows using a continuous laser dating system routinely yield analytical precisions of less than 0.45% (ls) on samples small than 0.5 mg. This is as good or better than has been obtained by any other method even though the sample mass is several orders of magnitude smaller. The system has the potential of resolving differences in apparent age of as little as 0.2% for high K/Ca samples as young as a few Ma. The analyses suggest that the seven volcanic units analyzed were erupted in an interval of about 0.1 m.y. or less. ¿ American Geophysical Union 1988