Perfectly round pearls are hard to come by. Only about 5-10% of cultured pearls are round. Consequently, this most desired shape is also the most expensive.

However, irregularly shaped pearls called baroque pearls can still be and are used effectively in jewelry designs. So if you "go for broke" or go all out with baroque pearls, the design is bound to be a winner because these pearls are more interesting than just plain round ones. They are not just for ordinary folks either but also fit for a royal crown. The former Empress Farah of Iran's coronation crown in 1967 seen here is graced with many of them.

Freshwater pearls are often baroque because they are started from small pieces of mantle tissue rather than a round mother-of-pearl starter bead as are seawater pearls. The most valuable of baroque pearls are the mostly dark coloured Tahitian seawater cultured pearls.

Wikipedia : Baroque Pearl
Pearls of Joy Company : Cultured Pearl Shapes