Priority Gas Auction (PGA)
A bidding war in which competing bots repeatedly outbid each other's gas price in the public mempool to get a profitable transaction mined first.
A priority gas auction happens when multiple bots detect the same profitable opportunity — such as an arbitrage trade or a liquidation — visible in the public mempool (see Kaavon's "Mempool" glossary definition), and compete to have their transaction included first by repeatedly resubmitting it with a higher gas price than the last competing bid. Because block space is limited and miners or validators historically prioritized higher-paying transactions, this created rapid, escalating bidding wars within seconds, often consuming most of the opportunity's profit in fees.
Priority gas auctions were especially prominent before the rise of private transaction relays and MEV-focused infrastructure, since any transaction broadcast to the public mempool could be seen and front-run (see Kaavon's "Front-Running" glossary definition) by competing searchers. Modern MEV infrastructure, including private order flow and builder-level auctions, has reduced how often ordinary users see public gas-price wars play out, by moving much of the competition for ordering off the public mempool entirely.
Examples
- A profitable arbitrage opportunity spotted in the public mempool can trigger a priority gas auction within seconds, as competing bots repeatedly rebid higher gas prices.
- Priority gas auctions can consume most of an opportunity's profit in gas fees, since competing bots keep bidding until the expected profit no longer justifies a higher bid.