An examination of the willingness to pay values elicited from more than 3000 persons involved in three independent studies revealed that the majority had offered one of a limited number of values from the ranges available to them. These values were 'prominent numbers', the use of which has been observed previously in circumstances where subjects feel that precise estimates of value are either difficult to make, or are not worth making. The existence of widespread prominence in response is suggestive of hypothetical bias in contingent valuation.