27-1. Ball Lost or Out of Bounds

If a ball is lost or is out of bounds, the player must play a ball,
under penalty of one stroke, as nearly as possible at the spot
from which the original ball was last played (see Rule 20-5).
Exceptions:
1. If there is reasonable evidence that the original ball is lost in
a water hazard, the player must proceed in accordance with
Rule 26-1.
2. If there is reasonable evidence that the original ball is lost in
an obstruction (Rule 24-3) or an abnormal ground condition
(Rule 25-1c) the player may proceed under the applicable Rule.

27-2. Provisional Ball
a. Procedure
If a ball may be lost outside a water hazard or may be out of
bounds, to save time the player may play another ball
provisionally in accordance with Rule 27-1. The player must
inform his opponent in match play or his marker or a fellowcompetitor
in stroke play that he intends to play a provisional
ball, and he must play it before he or his partner goes forward
to search for the original ball.
If he fails to do so and plays another ball, that ball is not a
provisional ball and becomes the ball in play under penalty of
stroke and distance (Rule 27-1); the original ball is lost.
(Order of play from teeing ground – see Rule 10-3)
Note: If a provisional ball played under Rule 27-2a might be
lost outside a water hazard or out of bounds, the player may
play another provisional ball. If another provisional ball is
played, it bears the same relationship to the previous
provisional ball as the first provisional ball bears to the
original ball.
b. When Provisional Ball Becomes Ball in Play
The player may play a provisional ball until he reaches the
place where the original ball is likely to be. If he makes a
stroke with the provisional ball from the place where the
original ball is likely to be or from a point nearer the hole than
that place, the original ball is lost and the provisional ball
becomes the ball in play under penalty of stroke and distance
(Rule 27-1).
If the original ball is lost outside a water hazard or is out of
bounds, the provisional ball becomes the ball in play, under
penalty of stroke and distance (Rule 27-1).
If there is reasonable evidence that the original ball is lost in a
water hazard, the player must proceed in accordance with
Rule 26-1.
Exception: If there is reasonable evidence that the original ball
is lost in an obstruction (Rule 24-3) or an abnormal ground
condition (Rule 25-1c) the player may proceed under the
applicable Rule.
c. When Provisional Ball to be Abandoned
If the original ball is neither lost nor out of bounds, the player
must abandon the provisional ball and continue play with
the original ball. If he makes any further strokes at the
provisional ball, he is playing a wrong ball and the provisions
of Rule 15 apply.
Note: If a player plays a provisional ball under Rule 27-2a, the
strokes made after this Rule has been invoked with a
provisional ball subsequently abandoned under Rule 27-2c
and penalty strokes incurred solely by playing that ball
are disregarded.