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 comparatively four mechanisms: Voluntary Contribution (VCM), Premium, Seed Money and Matching. The Premium and Matching mechanisms each generate higher contribution rate than VCM, while the gift size is not significantly different across mechanisms. Because this is one of the earliest embedded, web-based field experiments we report our methodology findings in some detail. Using pop-up windows and asking for non-privacy-invasive geographic information were ineffective as participant assignment techniques. Evidence of desire to donate inferred from participant clickstream data is a poor predictor of actual giving.http://deepblue.lib.umich.edu/bitstream/2027.42/49508/1/ipl05.pdf