The postal service of st. vincent, an island in the west indies, obtains a significant portion of its revenues from sales of special souvenir sheets to stamp collectors. the souvenir sheets usually contain several high-value st. vincent stamps depicting a common theme, such as the life of princess diana. the souvenir sheets are designed and printed for the postal service by imperial printing, a stamp agency service company in the united kingdom. the souvenir sheets cost the postal service $1.15 each. st. vincent has been selling these souvenir sheets for $10.00 each and ordinarily sells about 61,000 units. to test the market, the postal service recently priced a new souvenir sheet at $11.00 and sales dropped to 51,000 units.