The contribution sprang from diffi culties in ensuring quantitative sources for economic history of Slovene lands in Early Modern Times, and presents one of the reasons for this situation, namely the previously unknown custom of oral conclusion of contracts among peasants in the Karst region. At the beginning, it summarises the course of the judicial proceedings before the Devin/Duino court jury composed of the village community heads (županska pravda) in 1619–1620, and, subsequently, presents the custom itself (with the accompanying ritual) upon the purchase and sale of real estate among peasants. Finally, the paper highlights mostly economic aspects of the custom and suggests a periodization of the transition from oral to written practices in the Karst region.