Source: http://www.cisg.law.pace.edu/cisg/principles/uni16.html
Timestamp: 2019-04-26 03:38:16+00:00

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(b) if it was reasonable for the offeree to rely on the offer as being irrevocable and the offeree has acted in reliance of the offer.
1. Until a contract is concluded an offer may be revoked if the revocation reaches the offeree before he has dispatched an acceptance.
a. Article 16 CISG dealing with the revocation of an offer is a rather controversial provision of the Convention. Most of the difficulties derive from the different interpretative approaches of civil law and common law regarding the revocability of offers. While even the drafters of the CISG provision were determined to create a compromise solution between the approaches of the two systems, practical application of Article 16 CISG still reflects several ambiguities of interpretation.
b. Before examining whether the Official Comments to Article 2.4 of the UNIDROIT Principles may be used to help interpret Article 16 CISG, regard shall be paid to different approaches of civil and common law in interpreting revocation of the offer.
c. In civil law systems a contract is concluded only if the acceptance reaches the offeror. Before that, the offeror impliedly gives the offeree a reasonable time to consider the offer, during which time the offer is irrevocable unless otherwise indicated by the offeror. If the offer states a time limit for acceptance, the offer is usually irrevocable, and if it does not, the offer is irrevocable for a reasonable period.
d. In common law systems, however, the contract is concluded as soon as the offeree dispatches the acceptance. Prior to that point in time, the offer is revocable at any time, even if it must be accepted within a time period. This may sometimes also be the case even if the offeror expressly states that the offer is irrevocable.
e. The structure of Article 16 CISG mixes the two competing approaches. Delegates from civil law countries approved of laying down the general rule of revocability in Article 16(1) CISG. In turn, the civil law idea of irrevocability in situations where there is a fixed time for acceptance or irrevocability is otherwise indicated, was embodied in Article 16(2)(a). The second exception from the general rule of revocability, i.e., Article 16(2)(b) which is very similar to the principle of promissory estoppel, is also of common law nature. Although civil law systems similarly do not allow for revocation in bad faith (venire contra factum proprium), the wording of the CISG seemed unfamiliar to civil law lawyers. Some civil law characteristics are also recognizable in the application of the second exception to the revocability of offers, by the fact that it is applicable only if the offeree needs time to investigate whether or not he should accept the offer.
f. The wording of Article 2.4 of the UNIDROIT Principles is exactly the same as that of Article 16 CISG, yet each provision must be examined in its own context and the UNIDROIT Principles may not be the most appropriate auxiliary rules to help interpret a provision of the CISG, since there are many obstacles to overcome concerning the interpretation of both of these instruments. In spite of this, however, the applicability of the UNIDROIT provisions to Article 16 CISG cannot be excluded but it should be handled with special care.
g. The general rule of revocability of offers is set out in the provisions contained in Article 16(1) CISG and Article 2.4(1) UNIDROIT Principles, the latter literally taken from the former. The provisions lay down two conditions for revoking an offer: (i) the revocation must be made before the contract is concluded; and (ii) it must reach the offeree before he has dispatched an acceptance. Seemingly, these conditions must be applied concurrently, but in practice that could cause several ambiguities.
h. Let us see what happens if the offeror sends a letter of revocation to the offeree which the latter receives only shortly after he dispatched his letter of acceptance. The first condition, i.e., a revocation can be made only prior to the conclusion of the contract, is fulfilled because pursuant to Articles 23 and 18(2) CISG and Articles 2.1 and 2.6(2) UNIDROIT Principles, the letter of acceptance has not reached the offeror by the time the letter of revocation was received by the offeree. However, we come to a different conclusion if we examine the second condition, i.e., the letter of revocation is only effective if it reaches the offeree before he dispatches the letter of acceptance. In this case, it is evident that revocation would not be effective, either with regard to the CISG provision or to that of the UNIDROIT Principles.
i. Assuming the same situation with the difference that the offeree performs an act indicating assent instead of sending a letter of acceptance, pursuant to Articles 18(3) CISG and 2.6(3) UNIDROIT Principles, the contract is concluded upon the latter act and before the letter of revocation arrives. Therefore, the revocation is not effective even if the offeror is not yet aware of the act indicating assent. As the time period for revocation is restricted by the performance of an act, only the "contract-conclusion" condition is applicable in such cases.
j. In order to avoid such misunderstandings, scholars  suggest and the Official Comments on the UNIDROIT Principles [hereinafter: UNIDROIT Comments] equally express that the "contract-conclusion" condition should only be applied in the case of oral negotiations or acceptance by conduct without giving notice to the offeror. If the offer is accepted in writing, the latter condition is not applicable and the time limit for revocation is restricted until the offeree dispatches the acceptance while the contract itself is concluded only when the acceptance reaches the offeror. Commentaries to Article 16 CISG acknowledge that the latter method of interpretation might be disadvantageous to the offeror who can never be sure about whether revocation can be made in time, whether the offeree has already sent his acceptance or indicated his assent by performing an act.
k. Responding to this problem, Eörsi suggests that a higher level of good faith should be applied with regard to the rules of revocation by including into the wording of Article 16 CISG that "the offeree is bound to give notice if the revocation has reached him late". Until this might happen, the approach taken by the UNIDROIT Comments might be applied to the CISG but not by all means and not restrictively: "It is, however, justified in the view of the legitimate interest of the offeree in the time available for revocation being shortened." This view can be supported by the fact that it is the offeror who unilaterally gives the offeree the right to conclude the contract and that, unlike the offeree, the offeror has sufficient time before making an offer to weigh and asses the situation, possible risks and consequences. Of course, there might be situations where the offeror is forced to revoke an offer because of unexpected events, perhaps even independent of him, but those cases represent only a rather small part of all offers-acceptances. For instance, in the latter case, following the approach of the UNIDROIT Comments might not be appropriate because the legitimate interest of the offeror might collide with and actually prevail over that of the offeree. Thus, in such cases it is the legitimate interest of the offeror who will obviously be unable to perform a prospective contract, not to be forced to conclude such a contract because the offeree might have no chance to enforce performance. Of course, such subsequent impossibility of performance should be handled with care so as not to develop a malpractice where offerors can freely revoke an offer by referring to unexpected events or force majeure if they simply want to cancel the legal relationship with the offeree. Therefore, if we accept the approach set in the UNIDROIT Comments, each case must be examined separately and very carefully, and consistent trade and court practices must be developed.
In conclusion, it must be noted that in spite of the general principle of revocability, recent trends in national and international practice are towards strengthening irrevocability of offers.
l. Articles 16(2)(a)&(b) CISG and 2.4(2)(a)&(b) UNIDROIT Principles provide for one civil law and one common law exception from the general common law-rooted principle of revocability of offers.
m. A practical interpretation of this provision is not easy. The wording of the provision derives from the civil law countries' wish to incorporate a rule following their legal traditions but the wording is not unambiguous, which raises several questions.
n. The first problem is that for a common law attorney, indication of a fixed time for acceptance would only mean that the offer, which is still revocable, will lapse after that time, while for a civil law attorney, the offer is also irrevocable up until then. Furthermore, as wording of the CISG does not balance the two opposing views - this contradiction is enhanced even further when a legal relationship is exclusively between parties from a common law country or a civil law country - it allows revocation of offers in relationships between parties from common law countries. If the parties are from countries belonging to different legal systems, the communications and intentions of the parties, the exact circumstances of the particular case in the light of their dealing and usage of trade shall be taken into account in order to determine the status of the offer.
At this point it might be useful to supplement the CISG provisions on interpretation with the more detailed rules set out in Chapter 4 of the UNIDROIT Principles, dealing with interpretation of the contract. For example, by the interpretation of the intent, statements and conduct of the parties, besides negotiations, practices, usages and subsequent conduct, the nature and purpose of the contract and the meaning commonly given to terms and expressions in the trade concerned should also be taken into account. Such reference could perhaps assist in determining whether a particular offer was meant to be revocable or irrevocable.
o. Another problem concerning the indication of irrevocability contained in the offer relates to the wording used by the parties. It is undoubted that if an offer expressly states that it is irrevocable, then, pursuant to Article 16(2)(a), the offeror cannot revoke it. The question is, however, how should a statement of a time fixed for acceptance be interpreted, whether it by itself means that such an offer is irrevocable, and what "other ways" are appropriate for expressing irrevocability of an offer?
Expressing irrevocability in other ways can be inferred by determining the intent of the parties with regard to their statements and conduct. As suggested by the UNIDROIT Comments, this should be done case by case.
p. Concerning the indication of a fixed time for acceptance, some scholars believe that it makes the offer irrevocable, others like Honnold  deny such effect. Not even the UNCITRAL deliberations were unanimous because at one place automatic irrevocability in "fixed-time" cases is declared, and denied at another place. Malik suggests that "para (2) [of Article 16] is to be taken in the spirit of civil law whose rule it embodies", i.e., stating a fixed time should mean irrevocability. Yet, this should not be automatic and, in that, the Comments to the UNIDROIT Principles on Article 2.4(2)(a) serve as useful guidelines to interpret Article 16(2)(a) CISG. That includes that "the indication of a fixed time for acceptance may, but not necessarily, amount by itself to an implicit indication of an irrevocable offer. The answer must be found in each case through a proper interpretation of the terms of the offer in accordance with the various criteria laid down in the general rules of interpretation in Chapter 4 [UNIDROIT Principles]".
q. Here, again, besides Article 8 CISG, one could pay attention to the rules of interpretation of the UNIDROIT Principles in order to determine whether an offer, under Article 16(2)(a) CISG, shall be treated as revocable or irrevocable. Furthermore, distinction shall be made between stating a fixed date for acceptance as a simple expiration date, in which case the offer is not irrevocable during that time, and limiting the time for acceptance, meaning that such an offer is irrevocable.
r. Last but not least, even the UNIDROIT Comments repeat the above-mentioned problematic interpretation dichotomy that, beyond all other details, when interpreting the parties' intent concerning the revocability issue, legal traditions of the respective legal systems must be paid attention to. In other words, if the offeror comes from a country where fixing a time for acceptance indicates irrevocability then "it may be assumed" that the offer is considered to be irrevocable, and also the other way round with revocability. Although this suggestion does not serve the mandate of uniform interpretation of the CISG  very well, yet it is undeniable that in practice making an offer frequently relies upon domestic legal traditions. In this meaning, that last remark of the UNIDROIT Comments might not be helpful to interpret Article 16(2)(a) CISG.
s. The reliance provisions do not raise as many questions as do the previous ones. Pursuant to these provisions, an offer is also irrevocable if "it was reasonable for the offeree to rely on the offer as being irrevocable and the offeree has acted in reliance on the offer". These are two concurrent conditions upon which reasonable reliance on the offer is substantiated if, e.g., the offeree had a good reason to believe that the offer was irrevocable (e.g., as a result of the circumstances in case of urgent orders)  or if the offeror was aware that the offer was in connection with the fulfilment of another obligation on the offeree's side, and by performing acts like examining the offer, carrying out a costly investigation or preparing an offer to a third person.
t. The UNIDROIT Comments do not go any further than that, except for providing further examples of acts as a result of reliance. Among them the following are listed: making preparations for production, buying or hiring materials or equipment and incurring expenses - they can be useful in interpreting unclear CISG cases as well. Furthermore, the UNIDROIT Comments determine the general conditions of justifying such acts by stating that they must be regarded as normal in the trade concerned, or should otherwise have been foreseen by, or known to, the offeror. These conditions are also very useful in interpreting whether a certain act is justifiable under Article 16(2)(b).
The CISG provision is similar to the common law principle of promissory estoppel, but it also has some civil law characteristics since it is applicable only if the offeree needs time to investigate whether or not he should accept the offer.
As already mentioned above, applicability of the UNIDROIT Principles in the interpretation of the Convention's provisions is not the most appropriate method since the UNIDROIT Principles were not successful in eliminating difficulties appearing in the CISG. In spite of this, its applicability to the interpretation of the CISG cannot be fully excluded.
Article 16(1) CISG and Article 2.4(1) UNIDROIT Principles and the Comments on these Principles are in accord on most questions. The notion in the UNIDROIT Principles, suggesting that performing an act indicating acceptance can be disadvantageous to the offeror but it is justified in the view of the legitimate interest of the offeree, might be applied to interpreting the CISG.
In interpreting what is the fixed time for acceptance or another indication of irrevocability, it might be useful to supplement the provisions of Article 8 CISG with the application of Chapter 4 UNIDROIT Principles. On the other hand, the interpretation method suggested in the Official UNIDROIT Comments - i.e., that in determining whether an offer was meant to be revocable or irrevocable, special regard shall be paid to the legal traditions of the respective countries - if applied to the CISG could, in one sense, be said to undermine the mandate of uniform interpretation of the CISG. Yet, this is only one way of looking at the issue. Another way is to accept that autonomy of the parties, is one of the most fundamental principles of the CISG, and that the parties' intent  trumps the provisions of the Convention. In cases where the offeror and the offeree are both from common law countries or both from civil law countries (meaning similar legal traditions), the presumed intent of the parties should therefore play a role in the impact of Article 16(2)(b) CISG on Article 16(1). Rather than regarding this as an undermining of the mandate of uniform interpretation, a special kind of uniform interpretation will be present for parties from specific, and similar, legal backgrounds ... an interpretation that pays special heed to principles of party autonomy and presumed intent. Accordingly, it will be useful to pay attention to that where both parties are either from common law or civil law countries and, when examining a certain case, bearing in mind that uniform interpretation of the CISG is required, the latter should be carried out separately with regard to situations where both parties are from the same legal background (i.e., both common law or both civil law).
The Comments to Article 2.4(2)(b) UNIDROIT Principles, providing for the exact meaning and conditions of reliance, are useful in the interpretation of the counterpart CISG article as well.
* Master of Laws (in Hungarian law), University of Miskolc, Hungary, 2002. Ph.D. candidate at the Department of European Law and Private International Law, University of Miskolc, specializing in international business and investment law and international commercial arbitration. She is working on her Ph.D. thesis on jurisdictional issues in ICSID arbitration.
1. Burt A. Leete, Contract Formation under the United Nations Convention on Contracts for the International Sale of Goods and the Uniform Commercial Code: Pitfalls for the Unwary, at 'B', at <http://cisgw3.law.pace.edu/cisg/text/leete16.html#bl94>.
2. See Alejandro M. Garro, Reconciliation of Legal Traditions in the U.N. Convention on Contracts for the International Sale of Goods, II. 2., at <http://cisgw3.law.pace.edu/cisg/biblio/garro1.html>; Gyula Eörsi, Problems of Unifying Law on the Formation of Contracts for the International Sale of Goods, at <http://cisgw3.law.pace.edu/cisg/text/eorsi16.html>; Leete, supra note 1; Kazuaki Sono, Formation of International Contracts under the Vienna Convention: A Shift above the Comparative Law, Ch. 1., at <http://cisgw3.law.pace.edu/cisg/biblio/sono2.html>.
3. Garro, supra note 2; Leete, supra note 1; Kazuaki Sono, supra note 2.
4. Garro, supra note 2; Shahdeen Malik, Offer: Revocable or Irrevocable. Will Art. 16 of the Convention on Contracts for the International Sale Ensure Uniformity?, Ch. III. 2., at <http://cisgw3.law.pace.edu/cisg/biblio/malik.html>.
5. For a commentary on the equitable principle of estoppel as a general principle of the CISG, citing Art. 16 (2) (b) as an example - Art. 29 also - see Colin King, "The CISG - Another One of Equity's Darlings?", 8 Vindobona Journal of International Commercial Law and Arbitration (2004), 264-267.
6. Eörsi, supra note 2; Maria del Pilar Perales Viscasillas, The Formation of Contracts and the Principles of European Contract Law, Ch. VII, at <http://cisgw3.law.pace.edu/cisg/biblio/perales3.html>.
7. Leete, supra note 1, at "B".
8. The PECL, by way of contrast, took a different approach. Although a real balance between civil and common law principles could not be reached in either the Convention or the UNIDROIT Principles, the PECL managed to achieve this goal. Perales Viscasillas, supra note 6, Ch. 1. Perales Viscasillas explains here that the Principles of European Contract Law "achieved a set of rules balanced between the different principles that inspire both common law and civil law systems" not by selecting the "most appropriate rules" of the two different legal systems and not by summarizing the rules common to both of them. The PECL created a system of its own, built on the basis of enabling commercial exchange between the EU Member States and providing an autonomous interpretation of the rules of international trade and also influenced by trade practices.
9. "Caveat" in "Data on the pre-UNCITRAL legislative history of the CISG" at <http://cisgw3.law.pace.edu/cisg/text/roadmap/RoadmapL-16.html>.
10. Official Comments to Article 2.4. UNIDROIT Principles, Comment 1, op. cit.
11. These provisions are nearly the same, the CISG being a bit more specific in places.
See Article 23 CISG: "A contract is concluded at the moment when an acceptance of an offer becomes effective in accordance with the provisions of this Convention."
Cf. Article 2.1. UNIDROIT Principles: "A contract may be concluded either by the acceptance of an offer or by conduct of the parties that is sufficient to show agreement."
See also Article 18(2) CISG: "An acceptance of an offer becomes effective at the moment the indication of assent reaches the offeror. An acceptance is not effective if the indication of assent does not reach the offeror within the time he has fixed or, if no time is fixed, within a reasonable time, due account being taken of the circumstances of the transaction, including the rapidity of the means of communication employed by the offeror. An oral offer must be accepted immediately unless the circumstances indicate otherwise."
Cf. Article 2.6. (2) UNIDROIT Principles: "An acceptance of an offer becomes effective when the indication of assent reaches the offeror."
12. See Article 18(3) CISG: "However, if, by virtue of the offer or as a result of practices which the parties have established between themselves or of usage, the offeree may indicate assent by performing an act, such as one relating to the dispatch of the goods or payment of the price, without notice to the offeror, the acceptance is effective at the moment the act is performed, provided that the act is performed within the period of time laid down in the preceding paragraph."
Cf. Article 2.6. (3) UNIDROIT Principles: "However, if, by virtue of the offer or as a result of practices which the parties have established between themselves or of usage, the offeree may indicate assent by performing an act without notice to the offeror, the acceptance is effective when the act is performed."
13. Malik, supra note 3, Ch. III. 1; Fritz Enderlein & Dietrich Maskow, International Sales Law - United Nations Convention on Contracts for the International Sale of Goods, Commentary, at <http://cisgw3.law.pace.edu/cisg/biblio/enderlein-art16.html>.
14. Enderlein & Maskow, supra note 13; Eörsi, supra note 2.
15. Eörsi, supra note 2.
16. Comments to Article 2.4. UNIDROIT Principles, para 1 at http://cisgw3.law.pace.edu/cisg/principles/uni16.html>.
17. See Malik, supra note 4, Ch. II referring to recent trends in England, the United States (U.C.C., New York General Obligations Law) or Canada. In Chapter V, Malik also points out that for CISG to become the law of the future, a more liberal irrevocability approach should be taken. This would also serve the interest of developing countries which, in selling their raw materials, are very much dependant on far commodity markets which determine the prices of raw materials.
18. Eörsi, supra note 2; Leete, supra note 1, at "B".
19. Garro, supra note 2; Eörsi, supra note 2.
21. See Article 8 CISG, dealing with the interpretation of statements or other conduct of the parties.
22. Official Comments to Article 2.4. UNIDROIT Principles, Comment 2, op. cit.: "The answer must be found in each case through a proper interpretation of the terms of the offer in accordance with the various criteria laid down in the general rules on interpretation in Chapter 4."
23. J.D. Feltham, UN Convention on Contracts for International Sale of Goods, Journal of Business Law (1981), p. 339, 346; and S.K. Date Bah, UN Convention for Contracts for Sale of Goods: Overview", Rev. Ghana L., vol. 11 (1979), p. 50 at pp. 57-58, both cited by Malik, supra note 4, CH. III.2.
24. J. Honnold, Uniform Law for International Sales Under the 1980 United Nations Convention, Kluwer Academic, Netherlands, 1982, n. 34, p. 171.
25. See Malik, supra note 4, Ch. III.2.
26. See also Henry Mather, Firm Offers under the UCC and the CISG, Ch. II E., at <http://cisgw3.law.pace.edu/cisg/biblio/mather2.html>.
28. Mather, supra note 26.
29. See Article 7(1) CISG.
30. Mather, supra note 26, II. F, Enderlein & Maskow, supra note 13, at .
31. Mather, supra note 26, II. F; Malik, supra note 4, Ch. III.3.
32. Official Comments to Article 2.4. UNIDROIT Principles, Comment 2.
33. Leete, supra note 1, at "B". Furthermore, in Geneva Pharmaceuticals Tech. Corp. v. Barr Inc. the U.S. District Court expressed that promissory estoppel is actually different from what is written in Article 16(2)(b) CISG since the latter would preempt domestic law only if a plaintiff were to bring a promissory estoppel claim to avoid the need to prove the existence of a firm offer. The Court argued that "the latter did not expressly require that the offeree's reliance must have been foreseeable to the offeror and does not expressly require that the offeree's reliance be detrimental" resulting that the court dismissed the claim which was originally based on the promissory estoppel. The court also stated that the CISG establishing a modified version of promissory estoppel would contradict the CISG and stymie its goal of uniformity. See <http://cisgw3.law.pace.edu/cases/020510u1.html>. Pilar Perales Viscasillas opines that the Court failed to analyze the problem based on the core provisions of the CISG itself. She explains that the CISG governs contract formation either in a traditional offer-acceptance form or in other ways where sufficient agreement of the parties is present, and protection of the party relying ont the other party's statements or conduct is an inherent requirement of the CISG. Therefore, this latter principle is applicable to cases where "the promise and the acts done in reliance on the promise (statements or conduct made by the other party) are enough to show an indication of assent to a contract, i.e. an intention to be bound". It is also important to mention that such reliance cases do not equal precontractual liability which is not governed by the CISG. (See The Draft UNCITRAL Digest and Beyond: Cases, Analysis and Unresolved Issues in the U.N. Sales Convention - Papers of the Pittsburgh Conference Organized by the Center for International Legal Education (CILE), Franco Ferrari, Harry Flechtner & Ronald A. Brand eds., Sweet & Maxwell, Thomson, Sellier, 2004, p. 262-264.
A contrary decision was made in Vienna Arbitration proceeding SCH-4318 (Austria, 15 June 1994) where the tribunal held that although estoppel is not expressly settled by the CISG, it forms a general principle underlying the CISG (being "venire contra factum proprium"). See <http://cisgw3.law.pace.edu/cases/940615a4.html>.
34. Art. 6 CISG: "The parties may exclude the application of the Convention or [...] derogate from or vary the effect of any of its provisions." The principle of party autonomy ensconced in Art. 6 is arguably the most important general principle of the Convention. See <http://cisgw3.law.pace.edu/cisg/text/e-text-06.html>, for a presentation including legislative history as well as relevant doctrine and jurisprudence on that provision.
35. The intent of the parties can be derived by reference to the provisions in Art. 8 CISG, which deals with the intepretation of statements and other conduct of the parties, and Art. 9 CISG, which deals with usages and established practices applicable to the contract.
Para. (1) of this article, which is taken literally from Art. 16 CISG, states that until the contract is concluded offers are as a rule revocable.The same paragraph, however, subjects the revocation of an offer to the condition that it reach the offeree before the offeree has dispatched an acceptance. It is thus only when the offeree orally accepts the offer, or when the offeree may indicate assent by performing an act without giving notice to the offeror (see Art.2.6(3)), that the offeror's right to revoke the offer continues to exist until such time as the contract is concluded. Where, however, the offer is accepted by a written indication of assent, so that the contract is concluded when the acceptance reaches the offeror (see Art. 2.6(2)), the offeror's right to revoke the offer terminates earlier, i.e. when the offeree dispatches the acceptance. Such a solution may cause some inconvenience to the offeror who will not always know whether or not it is still possible to revoke the offer. It is, however, justified in view of the legitimate interest of the offeree in the time available for revocation being shortened.
Para. (2) provides for two important exceptions to the general rule as to the revocability of offers: (i) where the offer contains an indication that it is irrevocable and (ii) where the offeree, having other good reasons to treat the offer as being irrevocable, has acted in reliance on that offer.
The indication that the offer is irrevocable may be made in different ways, the most direct and clear of which is an express statement to that effect by the offeror (e.g. "This is a firm offer"; "We shall stand by our offer until we receive your answer"). It may, however, simply be inferred from other statements by, or conduct of, the offeror. The indication of a fixed time for acceptance may, but need not necessarily, amount by itself to an implicit indication of an irrevocable offer. The answer must be found in each case through a proper interpretation of the terms of the offer in accordance with the various criteria laid down in the general rules on interpretation in Chapter 4. In general, if the offeror operates within a legal system where the fixing of a time for acceptance is considered to indicate irrevocability, it may be assumed that by specifying such a fixed time the offeror intends to make an irrevocable offer. If, on the other hand, the offeror operates in a legal system where the fixing of a time for acceptance is not sufficient to indicate irrevocability, the offeror will not normally have had such an intention.
2. A invites B to submit a written offer of the terms on which B is prepared to construct a building. B presents a detailed offer containing the statement "Price and other conditions are not good after 1 September". If A and B operate within a legal system where such a statement is considered to be an indication that the offer is irrevocable until the specified date, B can expect the offer to be understood as being irrevocable. The same may not necessarily be the case if the offeree operates in a legal system where such a statement is not considered as being sufficient to indicate that the offer is irrevocable.
The second exception to the general rule regarding the revocability of offers, i.e. where "it was reasonable for the offeree to rely on the offer as being irrevocable", and the offeree has acted in reliance on the offer", is an application of the general principle of good faith and fair dealing laid down in Art. 1.7. The reliance of the offeree may have been induced either by the conduct of the offeror, or by the nature of the offer itself (e.g. an offer whose acceptance requires extensive and costly investigation on the part of the offeree or an offer made with a view to permitting the offeree in turn to make an offer to a third party). The acts which the offeree must have performed in reliance on the offer may consist in making preparations for production, buying or hiring of materials or equipment, incurring expenses etc., provided that such acts could have been regarded as normal in the trade concerned, or should otherwise have been foreseen by, or known to, the offeror.
3. A, an antique dealer, asks B to restore ten paintings on condition that the work is completed within three months and that the price does not exceed a specific amount. B informs A that, so as to know whether or not to accept the offer, B finds it necessary to begin work on one painting and will then give a definite answer within five days. A agrees and B, relying on A's offer, begins work immediately. A may not revoke the offer during those five days.
4. A seeks an offer from B for incorporation in a bid on a project to be assigned within a stated time. B submits an offer on which A relies when calculating the price of the bid. Before the expiry of the date, but after A has made the bid, B informs A that it is no longer willing to stand by its offer. B's offer is irrevocable until the stated date since in making its bid A relied on B's offer.

References: Art. 16
 Art. 16
 Art. 29
 v. 
 Art. 6
 Art. 6
 Art. 8
 Art. 9
 Art. 16
 Art.2
 Art. 2
 Art. 1