Detecting liquid in an acoustic flow meter. At least some of the illustrative embodiments are methods including flowing a gaseous substance through a central passage of a meter body, sending acoustic signals along respective chordal pathways across the central passage (none of the chordal pathways intersect a lower portion of the central passage where liquid, if present during flow of the gaseous substance, accumulates), calculating a flow velocity of the gaseous substance proximate to each chordal pathway based on transit times of the acoustic signals along the respective chordal pathways, and determining the presence of a liquid accumulated in the lower portion based on the flow velocity proximate to each chordal pathway.