et al. 2004; AFGL 618, Cox et al. 2003), have focused attention on the complex geometry of PN formation. The underlying mechanisms are not well understood, but they likely involve effects that influence the survival of, or affect the characteristics of, the molecular gas found in young PNe. Accordingly we have undertaken a deeper search for CO, especially in young PNe, to significantly extend the sample where the characteristics of the molecular gas are known.

Based on considerations of line opacity, atmospheric transparency, telescope beam size, and receiver sensitivity, the 230 GHz CO $J=2-1$ line is the optimal transition for CO searches of PN envelopes, where the emission is distributed on small angular scales and is optically thin, or partially thin, in most cases. In the time since our previous survey work, an important increase in capability at 230 GHz has been the development of multiple beam receivers. PNe are distributed close to the galactic plane, and a sensitive search in CO is inevitably contaminated by interstellar CO emission. The use of a multiple beam array on the IRAM 30 m telescope for the present survey observations proves to be a very efficient way to address this issue.

The plan 