Online price comparison sites (shopbots) like PriceGrabber.com are the most powerful tools for consumers to easily compare prices and find offers for desired products. Besides providing distributions of actual prices in price comparison tables, shopbots like NexTag.com have recently introduced price charts (line charts) displaying a product's full price history. Price charts should support consumers in forming expectations about future prices. Nevertheless, it is currently unclear how price charts influence consumer price expectations and purchase decisions. The results of this study show that the provision of past prices leads to strong adjustments of price expectations depending on price chart characteristics. In particular, the trend, variance and range of past prices in the chart strongly affect price expectations and purchase timing decisions. Furthermore, in the case of a strong downward trend and high variance in past prices, results show that nearly 50% of the total effect is caused by the visualization of the price history.