We implemented one of the first web-based online field experiments of fund-raising. We embedded our experiment in the Internet Public Library to test four mechanisms: Voluntary Contribution (VCM), Premium, Seed Money and Matching. Although the gift size is not significantly different across mechanisms, the Seed and Matching mechanisms each generate significantly higher user click-through response rate than the Premium mechanism. Because this is one of the earliest embedded, web-based field experiments, we report our methodology findings in some detail. Cookies work better as participant assignment techniques than pop-up windows and elicitation of geographic information. Participant clickstream data that nominally demonstrate a desire to donate is a poor predictor of actual giving.