Drupal and memory allocation

Hi

A query regarding a drupal site and memory allocation.

I have a client who has 3 domains sharing the same memory i.e. 128MB.

One of these sites is a drupal one and I have allocated 92MB to the drupal site using .htaccess.

Every now and then the drupal site shows me WSOD as do the other domains.

Looking at the memory usage in control panel it seems always near the limit.

So do we need our host to allocate more shared memory to eliminate WSOD occurrences?