This study analyzed out-of-stock (OOS) grocery store merchandise data from 661 retail outlets across 29 countries over 18 months. The study found that 4% of sales are lost due to missing items from shelves. A key finding was that 75% of OOS issues were caused by retail-level factors like underestimating demand, long ordering processes, and self-restocking practices rather than upstream supply chain issues. When OOS occurs, up to 43% of customers will shop at a different store and 7-25% may avoid the purchase altogether, representing significant losses for retailers.