Framework agreements (FAs) are procurement mechanisms commonly used by buying agencies around the world to satisfy demand that arises over a certain time horizon. This paper is one of the first in the literature that provides a formal understanding of FAs, with a particular focus on the cost uncertainty faced by bidders over the FA time horizon. We introduce a novel model that generalizes standard auction models to include this salient feature of FAs; we analyze this model theoretically and numerically. First, we show that FAs are subject to a sort of winner’s curse that induces higher expected buying prices relative to running first-price auctions as needs arise. Then, our results provide concrete design recommendations that alleviate this issue and decrease buying prices in FAs, highlighting the importance of (i) monitoring the price charged at the open market by the FA winner and using it to bound the buying price; (ii) investing in implementing price indexes for the random part of suppliers’ costs; and (iii) allowing suppliers the flexibility to reduce their prices to compete with the open market throughout the selling period. These prescriptions are already being used by the Chilean government procurement agency that buys US$2 billion worth of contracts every year using FAs.