This study analyzes tradeoffs online grocers face in their fulfillment strategy. Brick and click grocers initially favor fulfillment from stores rather than distribution centers. However, store fulfillment is vulnerable to congestion and "trolley rage" when pickers of online orders get in the way of traditional shoppers. Although fulfillment from distribution centers relieves store congestion, and improves picking productivity and product selection, online grocers show concern for the high cost and uncertain demand. We propose a model for minimizing congestion of online grocery orders. Practitioners can use the model to prevent customer dissatisfaction while researchers will find this study provides a basis for future model variants.