In 15 studies, positive word of mouth (PWOM) is more common than negative word of mouth (NWOM) in every case. The incidence ratio averages 3 to 1. Categories with high levels of NWOM tend to have high levels of PWOM, and individuals who produce NWOM also tend to produce PWOM. In follow-up studies, using two alternative measures of WOM, we confirm that PWOM occurs approximately three times as often as NWOM. Further exploratory studies indicate that most PWOM is about a consumer's main brand; as a consequence, the incidence of PWOM in a category is distributed according to brand market share. We discuss possible explanations for these results and develop six propositions to guide further research on word of mouth.