Short answer. Generally yes. Under Article 2020, the loser in a game that is not one of chance must pay his loss, provided no local ordinance prohibits betting on it. But the obligation is not unlimited: if the amount is excessive under the circumstances, the court shall reduce the loss to the proper sum.
What the law says
The loser in any game which is not one of chance, when there is no local ordinance which prohibits betting therein, is under obligation to pay his loss, unless the amount thereof is excessive under the circumstances. In the latter case, the court shall reduce the loss to the proper sum.
Civil Code, Article 2020 — Loss in a Game of Skill. Read the full provision →
Skill and chance are treated differently
The first question is what kind of game you bet on. The Code enforces bets on games of skill quite differently from bets on games of chance. A loss on a genuine game of chance — mere gambling — generally cannot be collected through the courts. A loss on a game that turns on skill is, by contrast, a recognised obligation: the law regards the outcome as a real contest rather than a throw of the dice, and holds the loser to his wager. So whether your game is one of skill or one of chance is the threshold that decides whether the debt is enforceable at all.
The obligation to pay, and its condition
Article 2020 states the duty with one important proviso: The loser in any game which is not one of chance, when there is no local ordinance which prohibits betting therein, is under obligation to pay his loss, unless the amount thereof is excessive under the circumstances. Two conditions therefore have to hold before you are bound. The game must not be one of chance, and no local ordinance may prohibit betting on it. If a valid ordinance in your locality forbids the wager, the obligation does not arise and the winner cannot enforce it there.
The court can cut down an excessive loss
Even where you are otherwise bound to pay, the Code builds in a safety valve: In the latter case, the court shall reduce the loss to the proper sum. This is an unusual power — courts do not normally rewrite the amount two competent parties agreed on — and it reflects the law's wariness of large losses run up over play. "Excessive under the circumstances" is judged against the situation as a whole, so what counts as excessive for one bettor need not for another. The reduction is not automatic; a court applies it when the sum demanded is out of proportion.
If you are asked to pay
Work through the same questions the law does. Was the game genuinely one of skill? Does an ordinance in your locality prohibit betting on it? And is the amount demanded excessive given your circumstances and the nature of the play? If a winner sues to collect, you are entitled to raise each of these, and in particular to ask the court to moderate a figure that is disproportionate. Keeping a clear record of what was actually wagered and agreed helps, because both the enforceability of the bet and any reduction of it turn on the concrete facts.