<p>Directed Acyclic Graph (DAG) blockchain applications represent an evolution from traditional linear blockchain solutions, addressing their inherent scalability issues. The analysis of the transactions fee market in these applications proves particularly insightful, given their demonstrated ability to manage very high transaction throughputs, and the crucial role transaction fees play in blockchain sustainability, efficiency and security, as a mechanism to incentivize validators and regulate network congestion.</p><p>This research addresses a gap by assessing the transactions' supply and demand characteristics and their influence on the related fees within the four largest DAG blockchain applications by market capitalization, namely Hedera, Kaspa, Iota and Conflux. The analysis reveals diverse approaches to transaction management across these applications, deriving from price and market entry regulation to open competition and unrestricted entry for miners, directly influencing the level and predictability of fees paid by users. Analysis of extensive datasets reveals a substantial surplus of space for transactions, with current throughput remaining well below effective limits. This oversupply explains the fractional transaction fees compared to Bitcoin. By introducing formal economic modelling and analysing key metrics, this research assesses transactional friction and economic sustainability across varying policies and consensus mechanisms. These findings provide practical insights for the design and evolution of DAG blockchains, offering detailed implications for policymakers and users to maintain competitive, sustainable participation and mitigate economic risks.</p> Graphical Abstract <p></p>