Building on earlier work by Estevadeordal (2000), we construct a synthetic index (R-index) intending to capture the restrictiveness of rules of origin in preferential trading agreements. The R-index is applied to NAFTA and the Single List of the EU's PANEURO system covering all of the EU's preferential trade agreements. The R-index highlights how a common set of rules of origin can affect countries differently depending on their export structures, and how their complexity varies across sectors. Having controlled for the extent of tariff preference at the tariff-line level, the R-index contributes to explain differences in the rate at which preferences are used. Finally, we compute estimates of the compliance costs associated with rules of origin under NAFTA and under PANEURO and find them to be between 6.8% of good value (NAFTA) and 8% (PANEURO).