Although preferential trade agreements (PTAs) have proliferated over the past 60 years, the formation or enlargement of a PTA remains a rare event. Among 10,585 country-pairs for 57 years (463,289 observations), there have been only 1,560 such events. While a small number of recent studies have examined empirically the economic determinants of the likelihood of a pair of countries having a PTA, this study explains empirically the timing of all PTA formations and enlargements from 1950 through 2006 using an econometric duration analysis. Our main and novel goal is to predict (in-sample) a substantive share of these 1,560 PTA events using a parsimonious model with only economic variables. Our analysis reveals that we can predict correctly the actual year of entry into force for 21 percent of the 1,560 bilateral PTA formations/enlargements in the period 1950-2006 among the 10,585 pairings of 146 countries using only a few economic variables. Moreover, we can predict correctly 48 percent of these PTA events within a 10-year window using this parsimonious model.