En Prison is a continuing-bet rule for roulette. When zero lands against a qualifying even-money wager, the stake is marked or recorded as “in prison” instead of being settled as an immediate full loss. A later spin decides whether the stake is released or lost under the table’s posted procedure.
The usual qualifying wagers are red/black, odd/even, and 1–18/19–36 on a single-zero wheel. Straight numbers, splits, streets, corners, six-lines, dozens, columns, and wheel-section combinations normally do not qualify.
The basic sequence
Suppose you wager $40 on red.
- The first spin lands zero. The $40 does not win. Under En Prison, the dealer marks it as unresolved rather than collecting it as an ordinary full loss.
- The next spin lands red. The imprisoned stake is released and returned. It normally earns no profit.
- Or the next spin lands black. The imprisoned stake is collected.
- If the next spin is zero again, the posted repeat-zero rule controls. The stake may remain imprisoned, lose, be divided, or receive another stated treatment.
The phrase “returned without profit” is central. A released $40 stake is not a $40 win. Across the original zero spin and the release spin, the player finishes at zero on that wager.
En Prison and La Partage solve zero differently
Both rules soften zero on qualifying even-money bets, but their procedures are not interchangeable.
| Rule | What happens when zero lands | Is another spin needed? | Typical immediate cash result |
|---|---|---|---|
| Ordinary single-zero roulette | Full stake loses | No | −100% of stake |
| La Partage | Half is collected and half returned | No | −50% of stake |
| En Prison | Stake is marked as unresolved | Yes | No final settlement yet |
La Partage closes the wager immediately. En Prison carries the wager into another result. That continuing state creates more procedure, more recordkeeping, and more room for house-rule differences.
New action and imprisoned action are separate
After a zero, a player may be permitted to place fresh wagers for the next spin while the old wager remains imprisoned. The two positions must not be confused.
Consider this sequence:
- $40 on red becomes imprisoned after zero;
- the player adds a new $20 wager on black;
- the next result is black.
Under a common full-stake En Prison procedure:
- the imprisoned red loses $40;
- the new black wager wins $20 profit;
- the net result from the two positions is −$20.
The black win does not “free” a red prison wager. The release condition follows the chance attached to the imprisoned stake, unless the table expressly permits the player to change that chance.
Some French-style rules do permit a change between equivalent even-money chances while the bet remains barred. That is a table rule, not a universal right. The dealer’s marker, terminal display, or written rules should identify the active chance before the next spin.
Which bets normally qualify
The standard even-money chances each cover 18 of the 36 nonzero numbers:
- red or black;
- odd or even;
- manque, meaning 1–18;
- passe, meaning 19–36.
Zero belongs to none of them. That is why zero can trigger special settlement.
| Bet family | Standard payout | Normally eligible? |
|---|---|---|
| Red/black | 1 to 1 | Yes |
| Odd/even | 1 to 1 | Yes |
| 1–18/19–36 | 1 to 1 | Yes |
| Dozen or column | 2 to 1 | No |
| Straight number | 35 to 1 | No |
| Split, street, corner, six-line | Varies | No |
| Proprietary side wager | Posted rule | Only if expressly stated |
A game labelled “French roulette” or “European roulette” does not guarantee En Prison. The rule must be posted, available in the help screen, or confirmed by the dealer.
Why the rule can reduce the edge
On a standard single-zero wheel, an even-money bet wins on 18 pockets and loses on 19. Without protection:
[ EV=\frac{18}{37}(+1)+\frac{19}{37}(-1)=-\frac{1}{37} ]
The house edge is:
[ \frac{1}{37}=2.7027% ]
En Prison changes the economic cost of the zero branch. Under a repeat-prison procedure where another zero leaves the wager unresolved, the imprisoned stake’s expected loss is one-half unit. The original spin reaches that state only on 1 of 37 outcomes, so:
[ EV=-\frac{1}{37}\times\frac{1}{2}=-\frac{1}{74} ]
[ House\ edge=1.35135% ]
This is the same long-run price as immediate half-loss treatment under La Partage, although the timing and variance of settlement differ.
For the full recursive derivation and alternative repeat-zero treatment, see house edge with En Prison.
If a second zero loses the wager
Not every En Prison game keeps the bet imprisoned after another zero. Suppose the first zero sends the bet to prison and the next spin settles as follows:
- 18 winning chance numbers: stake returned, net 0;
- 18 opposite chance numbers: full stake lost;
- zero: full stake lost.
The expected loss after entering prison is then (19/37) of a unit. Since prison is entered with probability (1/37):
[ EV=-\frac{1}{37}\times\frac{19}{37} =-\frac{19}{1369} ]
[ House\ edge\approx1.3879% ]
That is still better than the ordinary 2.7027% single-zero edge, but it is not exactly 1.35135%. A rules page that advertises En Prison without explaining the second-zero branch leaves out a material settlement detail.
Worked table sequence
A player puts $60 on even.
| Spin | Result | Status of original $60 | Cash movement |
|---|---|---|---|
| 1 | Zero | Marked En Prison | $0 final settlement |
| 2 | 22 | Released because 22 is even | $60 stake returned, $0 profit |
The player has not won $60. The original stake has simply survived the two-spin sequence.
If spin 2 had been 17, the imprisoned $60 would lose. If spin 2 had been zero, the dealer would apply the posted repeat-zero rule rather than improvising.
Multiple imprisoned wagers
A player can have more than one qualifying chance on the layout. For example, $20 may be on red and $20 on low when zero appears. Both positions can become imprisoned.
On the next spin, 14 red would satisfy both chances and release both stakes. A result of 20 black would lose both. A result of 5 black would lose red but release low.
Each position must therefore retain its own identity. One general prison marker is not enough if it becomes unclear which chips belong to which chance. Physical tables use approved markers and placement procedures; electronic games should display each continuing wager in the game history or active-bet panel.
What an official rule can look like
The Société des Bains de Mer European roulette leaflet describes a 37-pocket wheel and states that when zero occurs, even-money bets are barred. It gives the player an option to divide the bet or wait for the next spin, with the bet freed if it wins, and also says a player may change the chance while the bet remains barred. See the Monte-Carlo Société des Bains de Mer roulette rules.
That document is useful because it shows a real approved procedure. It should not be generalized to a casino whose posted rules use a different repeat-zero or chance-change treatment.
Dealer and terminal controls
En Prison creates an unresolved wager that crosses spin boundaries. Good control requires more than remembering what happened.
A live-table procedure should make clear:
- which bets qualify;
- when the dealer places the prison marker;
- whether the player may change the chance;
- whether new wagers may be added beside the imprisoned bet;
- what a second zero does;
- how a released stake is distinguished from a paid win;
- how the table closes or transfers unresolved prison bets.
On an electronic or automated game, the player should be able to verify:
- the qualifying wager and amount;
- the triggering zero result;
- the continuing status;
- the release or loss result;
- any new wager made for the second spin;
- the final balance adjustment.
If a dispute occurs, record the terminal number, game identifier, time, stake, first result, follow-up result, and displayed rule before leaving the machine. A remembered sequence is weaker evidence than the system’s game history.
Common misunderstandings
“My bet wins on the second spin.” Usually it is released without profit. The stake returns; no 1-to-1 win is added.
“En Prison applies to dozens and columns.” Normally it applies only to the six even-money chances.
“Every second zero leaves the bet in prison.” Not necessarily. Repeat-zero treatment varies.
“The rule changes the next result.” It changes settlement, not wheel probability.
“I can use a progression during the prison spin.” New action may be allowed, but it is a separate wager with separate exposure. A progression cannot change the underlying roulette odds.
“En Prison is always better than La Partage.” Their long-run edge can be equivalent, but cash timing, repeat-zero treatment, operational clarity, and player preference differ.
What to check before betting
A usable rule statement should answer five questions:
- Which wheel and wagers qualify?
- Does a zero imprison the full stake?
- What result releases the stake, and is profit paid?
- What happens on another zero?
- Can the chance be changed or new action added?
If those answers are unavailable, do not assume the most favorable version. Use the expected-loss calculator only after identifying the actual rule, because the difference between 1.35135%, 1.3879%, and 2.7027% comes from settlement, not from the name printed above the table.