Differences between bilateral and unilateral promises of sale

Property transactions frequently involve a preparatory phase during which the parties commit themselves before the final signing. This intermediate step may take two distinct forms: the unilateral promise to sell (promesse unilatérale de vente) or the bilateral promise to sell (promesse synallagmatique de vente). These legal instruments, although pursuing a similar objective of securing the future transaction, involve radically different mechanisms and legal consequences. Mastery of these distinctions conditions the contractual strategy and risk management of the parties concerned.

Legal nature of promises to sell

The unilateral promise to sell

The unilateral promise to sell is defined in Article 1124 of the French Civil Code, which provides that "a unilateral promise is the contract by which one party, the promisor, grants to the other, the beneficiary, the right to opt for the conclusion of a contract whose essential elements are determined". In the property context, this promise gives the beneficiary an exclusive option right over acquisition of the property, without any reciprocal commitment on its part. Applied to a gratuitous act, the mechanism of the promise is subject to its own conditions, set out in our guide on the promise of gift.

The legal mechanism rests on a fundamental asymmetry: only the promisor seller is irrevocably bound during the option period. The beneficiary has the right to acquire the property on the predefined terms, but remains free not to proceed. This contractual asymmetry explains why the unilateral promise is generally accompanied by payment of an immobilisation indemnity (indemnité d'immobilisation) by the beneficiary.

The promisor's commitment is absolute during the option period. The promisor may neither revoke the promise nor transfer the property to a third party, on pain of the sanctions provided for in Article 1124, paragraph 3, of the French Civil Code, which states that "a contract concluded in breach of the unilateral promise with a third party who knew of its existence is void".

The bilateral promise to sell

The bilateral promise, also called a compromis de vente (preliminary sale agreement), creates reciprocal and immediate obligations for both parties. The seller undertakes to sell and the buyer correlatively undertakes to buy the property on the terms stipulated. This reciprocity of commitments characterises the bilateral nature of the contract. A comparison of the two preliminary contracts from the standpoint of each party's obligations is set out in our article preliminary sale agreement or promise to sell.

Legally, the bilateral promise already constitutes the sale itself, subject to the fulfilment of any conditions precedent provided for. Transfer of ownership takes place by the mere exchange of consents, in accordance with the principle of solo consensu in French contract law. The subsequent notarial deed merely records the sale, which is already perfect, and gives it a certain date.

This characterisation has important practical consequences: from signature of the bilateral promise, the buyer becomes owner subject to a condition subsequent if the conditions precedent are not fulfilled. This intermediate situation explains why professionals often prefer the bilateral promise in order to secure the transaction definitively.

Mechanism of formation and performance

Decision-making process in the unilateral promise

The unilateral promise sets up a decision-making process in two distinct stages. The first phase is the signature of the promise itself, which binds only the seller. The second phase occurs when the beneficiary exercises the option, the moment at which the sale is definitively formed.

This two-stage structure gives the beneficiary a genuine period for reflection. The beneficiary may carry out the necessary checks, obtain financing and have surveys carried out, without risk of being blamed for any non-performance. Exercise of the option is a unilateral act of will that does not require the promisor's agreement.

Failure to exercise the option within the time allowed results in automatic lapse (caducité) of the promise. The immobilisation indemnity paid generally remains with the promisor as compensation, unless otherwise stipulated. This automatic effect avoids disputes over the assessment of fault or loss.

Synchronous performance of the bilateral promise

The bilateral promise creates immediate and correlated obligations for both parties. Each contracting party may require the other to perform its obligations, notably payment of the price by the buyer and delivery of the property by the seller. This reciprocity produces a contractual balance different from that of the unilateral promise.

Non-performance by one party opens to the other the classic legal remedies: termination of the contract, damages and specific performance. A defaulting buyer is exposed to termination of the sale and loss of the sums paid. Symmetrically, a seller who refuses to perform may be compelled to deliver the property or ordered to pay substantial damages.

Legal regime of conditions precedent

Common conditions precedent

Conditions precedent are an essential means of securing both types of promise. In property, they relate mainly to obtaining financing, the grant of building permission, clearance of pre-emption rights, or satisfactory technical surveys.

Article L. 262-9 of the French Construction and Housing Code requires certain particulars to be inserted in promises relating to new dwellings. These provisions apply to both types of promise, but how they fit together differs according to the nature of the commitment.

Failure of a condition precedent results in retroactive annihilation of the bilateral promise, each party returning to its previous position. In the unilateral promise, failure means that the beneficiary is unable to exercise its option, without this constituting contractual non-performance on its part.

Impact on legal certainty

The mechanism of conditions precedent offers enhanced legal certainty in complex transactions. It allows the contract to be adapted to the specific features of each operation while preserving the legitimate interests of the parties. This flexibility explains their systematic use in professional practice.

Inserting a condition precedent of obtaining a loan deserves particular attention. In a bilateral promise, this condition protects the buyer against the risk of financial default while maintaining the seller's commitment. In a unilateral promise, it offers additional protection to the beneficiary, who in any event remains free not to exercise the option.

Financial consequences and guarantees

Regime of the immobilisation indemnity

The unilateral promise is generally accompanied by payment of an immobilisation indemnity by the beneficiary. This indemnity compensates the promisor's unilateral commitment and is the price of the option granted. Its amount, freely negotiable, traditionally ranges between 5% and 10% of the sale price.

The immobilisation indemnity has a dual regime depending on the outcome of the promise. If the option is exercised, it is generally set against the final sale price. If the beneficiary renounces or the promise lapses, it remains with the promisor without any need to justify a particular loss.

This mechanism offers financial predictability appreciated by the parties: the promisor receives flat-rate compensation for being tied up, while the beneficiary knows in advance the maximum cost of its renunciation.

Security deposit in bilateral promises

The bilateral promise usually provides for payment of a security deposit by the buyer, distinct in nature and effects from the immobilisation indemnity. This deposit, commonly set at 5% or 10% of the price, is an advance payment on the sale price and guarantees performance of the buyer's obligations.

The fate of the security deposit depends on the outcome of the transaction. On normal performance, it is set off in full against the price on signature of the notarial deed. Where the buyer fails to perform its obligations, notably by not signing the final deed without that being justified by the failure of a condition precedent, the deposit may be kept by the seller as liquidated damages. The regime of this sum, from payment to return, is detailed in our article on the security deposit on a property purchase.

This difference in regime significantly affects the financial balance of the two types of promise and often guides the parties' choice according to their appetite for risk.

Notarial security and land registration

Registration formalities

Promises to sell, whether unilateral or bilateral, must comply with certain registration formalities when they are recorded in a notarial deed or when their duration exceeds eighteen months. These formalities aim to ensure enforceability against third parties and to prevent fraud.

Registration with the land registration service (service de publicité foncière) gives promises a certain date and enforceability against all (erga omnes). This publicity is particularly important for unilateral promises, breach of which by the promisor in favour of a third party may be penalised by nullity of the competing contract, in accordance with the provisions of Article 1124 of the French Civil Code.

The bilateral promise benefits from reinforced protection by its very nature: as it already constitutes the sale, it immediately transfers ownership and makes any later transfer of the property to a third party impossible. This structural difference influences the securing strategy adopted by practitioners.

Involvement of the notary

The involvement of the notary has specific advantages depending on the type of promise chosen. For unilateral promises, it guarantees the legal certainty of the drafting and facilitates the publicity formalities. The notary checks in particular the validity of the conditions precedent and the balance of rights and obligations.

In bilateral promises, the notary's role extends to immediate verification of the conditions of validity of the sale: capacity of the parties, existence and legal availability of the property, compliance with planning rules. This early verification significantly reduces the risk of later litigation.

The notarial deed also confers particular evidential force and enforceability. Where one of the parties defaults, the other has a title allowing direct enforcement without prior proceedings to establish the debt.

Contractual strategy according to the type of transaction

Criteria for choosing between the two promises

The choice between a unilateral promise and a bilateral promise depends on objective factors linked to the nature of the transaction and the parties' interests. Complex transactions requiring thorough prior studies point towards the unilateral promise, which preserves the decision-making freedom of the potential buyer.

Transactions involving atypical property, requiring technical surveys or particular administrative authorisations, benefit from the flexibility of the unilateral promise. The buyer may carry out the necessary investigations without legal risk, while the seller receives compensation for being tied up.

Conversely, transactions involving standardised property, in a seller-friendly market, often favour the bilateral promise. This formula secures the sale immediately and avoids the risk of the buyer withdrawing for reasons not provided for in the contract.

Adaptation to financing constraints

The financing arrangements significantly influence the choice of type of promise. A buyer with sufficient own funds may enter into a bilateral promise without risk of default. This situation reassures the seller and may justify a favourable price negotiation.

Conversely, a buyer dependent on complex financing (multiple loans, support schemes, tax-driven structures) will generally prefer a unilateral promise with protective conditions precedent. This approach avoids exposure to damages if the financing structure fails.

Property professionals adapt their practices to these constraints by proposing sophisticated conditions precedent clauses, particularly in bilateral promises, in order to reconcile legal certainty with the economic feasibility of transactions.

Specific disputes and case law

Disputes relating to unilateral promises

Disputes over unilateral promises frequently concern the validity of the exercise of the option and compliance with time limits. Case law requires a clear and unequivocal exercise of the option, expressed in the form and within the time limits provided for in the contract. A late or ambiguous exercise of the option can have no legal effect.

The question of the promisor's withdrawal is another source of disputes. Before the 2016 reform of contract law, case law accepted that the promisor could withdraw by paying damages. Article 1124 of the French Civil Code clarified this situation by penalising with nullity any sale concluded with a third party in breach of a unilateral promise.

Disputes also concern the fate of the immobilisation indemnity where a condition precedent fails. Case law distinguishes according to whether the failure results from an event independent of the parties' will or from the wrongful conduct of one of them.

Disputes over bilateral promises

Bilateral promises generate specific disputes linked to their nature as a perfect sale. Disputes concern in particular specific performance of the contract and the assessment of damages for non-performance. The buyer may seek compulsory delivery of the property, unless physical or legal impossibility.

Termination of the bilateral promise follows the general rules of contract law. It may be ordered for non-performance of essential obligations, but generally requires prior formal notice. Damages may include loss of a chance and non-pecuniary loss, particularly in residential acquisitions.

Conditions precedent are strictly interpreted by the courts. Their fulfilment must be assessed objectively, without regard to the parties' subjective motives. A condition precedent deemed fulfilled can no longer be invoked to escape contractual obligations.

Frequently asked questions

Can a unilateral promise be turned into a bilateral promise?

The change requires the express agreement of the parties, evidenced by an amendment or a new contract. This modification fundamentally changes the nature of the commitments and must be accompanied by a renegotiation of the financial terms, notably the fate of the immobilisation indemnity, which loses its justification.

What is the optimal duration of a unilateral promise to sell?

The duration depends on the complexity of the transaction, generally between two and four months for ordinary transactions. A duration of more than eighteen months triggers particular registration formalities. An excessive duration may be recharacterised by the courts as a right of first refusal agreement (pacte de préférence).

Can the buyer assign its right in a unilateral promise?

Whether the option right can be assigned depends on the contractual stipulations. In the absence of a contrary clause, the right may be assigned, but the assignment must comply with any approval conditions provided for and does not change the obligations of the original promisor.

What happens if the property is destroyed before the final signing?

In a bilateral promise, destruction of the property places the risk on the buyer, who is already owner, unless there is insurance or a contrary clause. In a unilateral promise, destruction makes it impossible to exercise the option and releases the parties from their obligations.

Do promises to sell necessarily require the involvement of a notary?

Notarial involvement is not legally compulsory for promises, but it becomes necessary for the final deed of sale. However, the notarial deed offers greater legal certainty and facilitates the land registration formalities.

How is the immobilisation indemnity calculated in a unilateral promise?

The amount is freely negotiable between the parties. Practice generally places this indemnity between 5% and 10% of the sale price. It must be proportionate to the period of immobilisation and the promisor's potential loss.

Can a bilateral promise be terminated by mutual agreement?

The parties may always agree to an amicable termination, even of a bilateral promise. The termination must follow the forms provided for in the original contract and organise the terms for return of the sums paid and reimbursement of the costs incurred.

The choice between a unilateral promise and a bilateral promise conditions the contractual balance and the allocation of risks in property transactions. The unilateral promise favours the flexibility and security of the potential buyer, while the bilateral promise provides the stability and predictability sought by sellers. This strategic decision must take into account the specific features of each transaction, the financing constraints and the parties' wealth objectives. Before any commitment, a thorough legal analysis of the issues and consequences is needed in order to optimise the securing of the transaction envisaged.