The technique of pit-depth modulation is applied to optical data storage. Pits of M possible depths are written end-to- end to form a groove encoding log2(M) bits in each mark. Data was encoded onto discs with CD dimensions using standard photoresist mastering and replication methods. Methods for removing inter-symbol interference are demonstrated on pits as short as 0.6 micrometers . A 6-level pattern of 0.6 micrometers pits was read by an optical head from a 6X CD-ROM drive and the original levels were recovered with a standard deviation of approximately 6% of the dynamic range. A system prototype read data encoded as 4-level 0.8 micrometers pits with a raw bit error rate of 3 X 10-4.