Can a Zero-Fee Transaction Still Be Confirmed on a Congested Network?

Confirmation is highly unlikely but still possible, even on a congested network. During congestion, the competition for block space is high, and miners prioritize transactions with competitive fees.

A zero-fee transaction would only be included if a miner specifically chooses to include it, perhaps due to a direct arrangement or if the miner is the sender. For a typical user, a zero-fee transaction will likely remain in the mempool indefinitely during congestion.