When can I play a provisional ball, and what must I say?

Under Rule 18.3 of the 2023 Rules of Golf, you may play a provisional ball to save time when your ball might be lost outside a penalty area or might be out of bounds. This includes when the original ball has not been found and identified yet, or might be lost in a penalty area but also somewhere else on the course.

You must announce it before you play. Use the word "provisional" or otherwise clearly indicate you are playing under Rule 18.3. Saying only "I'm playing another ball" or "I'm playing again" is not enough. If you do not announce it, the ball you play is your ball in play under penalty of stroke and distance (Rule 18.1). If no one is nearby to hear you, you may play the provisional ball and then tell someone when you can.

A provisional ball is played under penalty of stroke and distance, from where your previous stroke was made. It is different from playing two balls when unsure of a ruling (Rule 20.1c).