A run-length-limited code, designated 3Φ(1,7), has been applied to optical disc recorders for the purpose of increasing the information capacity of a disc. The 3Φ(1,7) code was selected by an organized search of an extensive collection of NRZ-like, phase, and run-length-limited codes. Theoretical examination indicated that greater than a 20% linear packing density increase could be expected under the conditions that the recorder was forming the smallest pits possible. The factors which led to this conclusion and the properties of the 3Φ,7) code are discussed. Details of an experimental verification of the conclusions reached herein are presented in a companion paper, "Implementation of 3Φ(1,7) code for improving packing density on optical disc recorders," by P. Hess and J. Waring.