Asked by: Amanda Davies, King's Lynn
The current record, in English at least, is 637 words per minute, a record held by English comedian and presenter Steve Woodmore. That's about four times faster than most people talk and twice as fast as we can read. The practical limit on speech is comprehension. Beyond 300 words per minute, you can't really make out the individual words clearly – record attempts are adjudicated by recording the speech and playing it back more slowly.
The theoretical upper limit on speed would be the rate at which the facial muscles can contract. Muscle fibres can't contract faster than about five times per second, so if you are repeating the mouth-stretching words "wow oh wow oh", your lips couldn't manage to open and close more than 300 times per minute. Alternating between different muscles might let you interleave more words but 637 definitely looks like it's quite close to the natural limit.