Short answer. Yes. Under Article 1479, a promise to buy and sell a determinate thing for a price certain is reciprocally demandable. Because both sides have bound themselves — one to buy, the other to sell — either party can compel the other to go through with the deal, even before any deed of sale is signed.
What the law says
A promise to buy and sell a determinate thing for a price certain is reciprocally demandable.
Civil Code, Article 1479 — Mutual Promises to Buy and Sell, and Option Money. Read the full provision →
A two-sided promise binds both people
Article 1479 opens by saying that a promise to buy and sell a determinate thing for a price certain is reciprocally demandable. The key word is reciprocally. When one person promises to buy and the other promises to sell the same identified thing at an agreed price, each has given the other an enforceable right. If the would-be seller backs out, the buyer may go to court to compel the sale or claim damages; if the buyer backs out, the seller has the mirror-image remedy. The commitment runs both ways, which is exactly why the law treats a genuine two-sided promise as something you can enforce rather than a mere expression of interest.
The thing and the price must be fixed
The promise is demandable only if two elements are settled. The thing must be determinate — a specific, identified object, not a vague description that could point to several things. And the price must be certain — a definite amount, or at least fixed by a method the parties agreed on that needs no fresh negotiation to compute. If the parties are still haggling over which unit is being sold, or have not truly closed on a figure, there is no demandable promise yet, only ongoing talks. This is what separates a binding mutual promise from the preliminary back-and-forth that precedes many sales and commits no one.
How it differs from a one-sided option
Article 1479 draws a sharp line between a mutual promise and a one-sided one. A mutual promise — both buying and selling — is demandable on its own. But the same article adds that an accepted unilateral promise, where only one side is bound while the other stays free to decide, binds the promisor only if it is supported by a consideration distinct from the price, commonly called option money. So if only the seller promised to sell and you gave nothing separate for that promise, your position is weaker than if both of you had promised. When both are truly committed, no separate option money is needed.
What enforceability does not guarantee
Being demandable does not mean the deal is beyond challenge. The promise must still rest on real consent; if it was obtained by fraud, mistake, or intimidation, it can be attacked like any contract. Form can also matter for proof: a promise involving real property may need to be in writing to be enforced in court under the Statute of Frauds, even though it is not void. And enforceability speaks to compelling the sale, not to who owns the thing in the meantime — ownership normally passes on delivery. Within those limits, though, a clear mutual promise to buy and sell a specific thing for a fixed price is something the courts will hold both sides to.